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Math I · Mathematics
Transformations and similarity · Geometric transformations

Translations

Before you start, make sure you know: Pythagorean Theorem (Math 7)

In a video game, you tap "3 spaces right, 2 spaces up" and your character slides across the screen. Every part of the character moves the same amount in the same direction, so nothing turns, stretches, or flips. That is a translation. How can we describe it with just two numbers, and how far did the character really travel? By the end of this page you will know.

Translations and vectors

A vector is described by its components: how far it goes horizontally and how far vertically. We write them $\langle a, b\rangle$. Some problems write them with parentheses, $(a, b)$. It means the same thing.

$$\vec{AB} = \langle x_B - x_A,\ y_B - y_A\rangle \qquad \text{"end minus start"}$$

The magnitude (length) of $\vec v = \langle a, b\rangle$ comes from the Pythagorean Theorem:

$$|\vec v| = \sqrt{a^2 + b^2}$$ Vector from A(2, 1) to B(6, 4) on a coordinate grid: 4 units right and 3 units up, so the components are 4 and 3 and the magnitude is 5. A(2, 1)B(6, 4) +4+3 Components: (6−2, 4−1) = (4, 3) Magnitude: √(4² + 3²) = 5

Not every motion is a translation. Sliding a drawer open is one: every point of the drawer moves straight, the same amount. Turning a key is not, because it rotates. A mirror reflection is not either, because it flips the picture.

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Identify which of the following options correctly describes a translation: a) Turning a key in a lock. b) The movement of a drawer when opening it. c) The reflection of…

Identify which of the following options correctly describes a translation:

  1. a) Turning a key in a lock.
  2. b) The movement of a drawer when opening it.
  3. c) The reflection of a mountain in a lake.
  4. d) The movement of the hands of a clock.
Solve
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Look at the grid and determine the components of the translation vector $\vec{u}$ that allows moving the point $P$ to the position of the point $P'$.

Look at the grid and determine the components of the translation vector $\vec{u}$ that allows moving the point $P$ to the position of the point $P'$.

O +5 +3 u P P'
Solve
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In a video game, a character is at point $C(5, -2)$. The player presses a key combination that is equivalent to a translation. If the character suddenly appears at point…

In a video game, a character is at point $C(5, -2)$. The player presses a key combination that is equivalent to a translation. If the character suddenly appears at point $C'(1, 3)$, what is the translation vector $\vec{w}$ that has acted?

Solve

Translating points and figures

Why does it work? The vector says "move $a$ horizontally and $b$ vertically." Adding $a$ to $x$ moves the point left or right. Adding $b$ to $y$ moves it up or down. A positive $a$ goes right and a negative $a$ goes left. A positive $b$ goes up and a negative $b$ goes down.

Drag the sliders and watch: every point moves the same amount, and the figure keeps its shape and size.

A triangle with vertices (1, 1), (4, 1), (2, 4) and its image after the translation by the vector 5 right and 2 up, with dashed arrows from each vertex to its image. Original Image v = ⟨5, 2⟩
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A surveillance drone takes off from a control point and makes a linear movement defined by the vector $\vec{v} = (5, -3)$. If the starting point has coordinates…

A surveillance drone takes off from a control point and makes a linear movement defined by the vector $\vec{v} = (5, -3)$. If the starting point has coordinates $A(2, 4)$ on the control center map, what will be the coordinates of the point $A'$ where the drone is located after making this movement?

Solve
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Given the line segment with endpoints $A(-3, 1)$ and $B(1, 2)$, calculate the coordinates of the transformed line segment $A'B'$ after applying a translation by vector…

Given the line segment with endpoints $A(-3, 1)$ and $B(1, 2)$, calculate the coordinates of the transformed line segment $A'B'$ after applying a translation by vector $\vec{v} = (4, 3)$. Represent both line segments on a set of coordinate axes.

Solve

Working backward

Sometimes you know the image and need the vector, or the preimage.

This is just the translation rule solved for the unknown, the same way you undo addition with subtraction.

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If we translate the point $Q$ by the vector $\vec{v} = (-4, 7)$ we obtain the point $Q'(0, 2)$. What were the coordinates of the original point $Q$ before the…

If we translate the point $Q$ by the vector $\vec{v} = (-4, 7)$ we obtain the point $Q'(0, 2)$. What were the coordinates of the original point $Q$ before the translation?

x y 0 +7 −4 v = (−4, 7) Q(?, ?) Q'(0, 2)
Solve
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In a graphic design application, a teenager is creating a logo. They have drawn a triangle with vertices at $P(2, -1)$, $Q(5, 0)$ and $R(3, 4)$. To complete the design,…

In a graphic design application, a teenager is creating a logo. They have drawn a triangle with vertices at $P(2, -1)$, $Q(5, 0)$ and $R(3, 4)$. To complete the design, they need to translate the triangle so that vertex $P$ is situated at the origin $O(0, 0)$.

  1. a) State the components of the translation vector $\vec{v}$ that must be applied.
  2. b) Calculate the new coordinates of the vertices $Q'$ and $R'$ after applying this translation.
Solve
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An equilateral triangle has its vertices at the points $A(0, \sqrt{3})$, $B(-1, 0)$ and $C(1, 0)$. It undergoes a translation that maps the centroid of the triangle to…

An equilateral triangle has its vertices at the points $A(0, \sqrt{3})$, $B(-1, 0)$ and $C(1, 0)$. It undergoes a translation that maps the centroid of the triangle to the origin $O(0, 0)$.

Note: The centroid of a triangle with vertices $(x_1, y_1), (x_2, y_2), (x_3, y_3)$ is calculated as $(\frac{x_1+x_2+x_3}{3}, \frac{y_1+y_2+y_3}{3})$.

  1. Calculate the coordinates of the original centroid $G$.

  2. Determine the necessary translation vector $\vec{v}$.

  3. Calculate the new coordinates of the vertices $A', B'$ and $C'$.

−1 1 1 2 A B C G A' B' C' O v
Solve

Composing translations

Do one translation by $\vec u$, then another by $\vec v$. The result is the same as a single translation by the sum of the vectors:

$$\vec u + \vec v = \langle u_1 + v_1,\ u_2 + v_2\rangle$$

Going along $\vec u$ and then along $\vec v$ ends in the same place as going straight along $\vec u + \vec v$.

Two vectors placed head to tail, u = (5, 1) and then v = (2, 3), and the dashed vector from the start to the end, u + v = (7, 4). u = ⟨5, 1⟩ v = ⟨2, 3⟩ u + v = ⟨7, 4⟩ Going along u, then v = going straight along u + v

The order does not matter: $\vec u + \vec v = \vec v + \vec u$.

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An object undergoes two consecutive translations. The first is defined by the vector $\vec{u} = (2, 5)$ and the second by the vector $\vec{v} = (3, -1)$. What is the…

An object undergoes two consecutive translations. The first is defined by the vector $\vec{u} = (2, 5)$ and the second by the vector $\vec{v} = (3, -1)$. What is the vector of the single translation that is equivalent to performing the two previous ones in succession?

Solve
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A surveillance drone takes off from a base located at point $A(-4, 1)$ on a coordinate system. To carry out its first patrol, it moves following the translation vector…

A surveillance drone takes off from a base located at point $A(-4, 1)$ on a coordinate system. To carry out its first patrol, it moves following the translation vector $\vec{u} = (6, 3)$. After a pause, it makes a second movement defined by the vector $\vec{v} = (-2, 5)$.

  1. a) Calculate the coordinates of the final point where the drone is located after the two movements.
  2. b) Determine the components of a single vector $\vec{w}$ that represents the direct displacement from the take-off point to the final position.
X Y 0 +6 +3 −2 +5 A(−4, 1) B C (Final) u(6, 3) v(−2, 5) w
Solve
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A surveillance drone departs from a base located at point $B(12, 15)$. It makes a first displacement following the vector $\vec{u} = (-8, 4)$ to position itself over a…

A surveillance drone departs from a base located at point $B(12, 15)$. It makes a first displacement following the vector $\vec{u} = (-8, 4)$ to position itself over a target. After completing the mission, it receives an emergency displacement order via the vector $\vec{v} = (5, -10)$.

  1. Calculate the final coordinates of the drone after both movements.

  2. Determine the single translation vector $\vec{w}$ that would allow the drone to return directly from its final position to the base $B$ in a single movement.

  3. If each unit on the grid represents $10$ feet, calculate the total distance (modulus) it would travel on that return journey.

5 10 15 5 10 15 20 0 Δx=3 Δy=6 B(12, 15) P₁(4, 19) P₂(9, 9) u = (−8, 4) v = (5, −10) w = (3, 6)
Solve

Inverse translations and the identity

The inverse of the translation by $\vec v = \langle a, b\rangle$ is the translation by $-\vec v = \langle -a, -b\rangle$. It undoes the move and brings every point back where it started.

Doing a translation and then its inverse gives the sum $\vec v + (-\vec v) = \langle 0, 0\rangle$. This is the identity translation: nothing moves at all.

The same idea works with more vectors. If several translations add up to $\langle 0, 0\rangle$, a figure ends exactly where it started.

Three vectors placed head to tail that form a closed triangle and return to the starting point, so their sum is the zero vector. u v w Start = End u = ⟨2, 1⟩ v = ⟨−5, 3⟩ w = ⟨3, −4⟩ u + v + w = ⟨0, 0⟩
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Two translations are said to be inverse if, when applied one after the other, the final point coincides with the initial point (the identity is obtained). a) If an…

Two translations are said to be inverse if, when applied one after the other, the final point coincides with the initial point (the identity is obtained).

  1. a) If an object has been translated by the vector $\vec{v} = (-7, 4)$, what is the vector of the inverse translation?
  2. b) If we apply the translation $\vec{u} = (3, -2)$ to the point $M(x, y)$ and then its inverse, what are the coordinates of the resulting point?
  3. c) A boat moves from the port $A(10, 20)$ to a buoy $B$ by means of the vector $\vec{v} = (50, -30)$. Due to a storm, it must return immediately to the port. What translation vector must it follow to return exactly to the point $A$?
Solve
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On a Cartesian plane, a figure is first translated by the vector $\vec{u} = (2, -3)$ and then by an unknown vector $\vec{v} = (v_x, v_y)$. The resulting translation…

On a Cartesian plane, a figure is first translated by the vector $\vec{u} = (2, -3)$ and then by an unknown vector $\vec{v} = (v_x, v_y)$. The resulting translation (composition) is a translation that leaves all the points of the y-axis ($Y$-axis) now situated on the line $x = 5$.

  1. Determine the composite vector $\vec{w} = \vec{u} + \vec{v}$.

  2. Find the components of the vector $\vec{v}$.

  3. If we apply the inverse translation of $\vec{v}$ to the point $Q(0, 0)$, at what point is it situated?

Solve
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A movement in the plane is defined as the composition of three successive translations defined by the vectors $\vec{a} = (3, -1)$, $\vec{b} = (-5, 4)$ and…

A movement in the plane is defined as the composition of three successive translations defined by the vectors $\vec{a} = (3, -1)$, $\vec{b} = (-5, 4)$ and $\vec{c} = (2, -3)$.

  1. Show analytically that this composition of movements is equivalent to the identity translation.

  2. What does it mean geometrically for the result to be the identity?

  3. If a square with an area of $16$ square units undergoes these three translations, what will its final area be? Justify your answer based on the properties of isometries.

X Y Area = 16 u² a(3,-1) b(−5,4) c(2,-3) O(0,0) Identity Translation a + b + c = (0,0)
Solve

What a translation preserves

A translation is a rigid motion (also called an isometry). The image is exactly the same shape and size as the original, only in a new place.

Why are distances preserved? Both endpoints move by the same $\langle a, b\rangle$, so the horizontal and vertical differences between them do not change: $(x_2 + a) - (x_1 + a) = x_2 - x_1$, and the same for $y$. The distance formula then gives the same number.

Segment AB and its translated image A'B' form a parallelogram: they are parallel and have the same length, and the dashed segments AA' and BB' are equal. AB A′B′ AB ∥ A′B′ and AB = A′B′

Notice that the picture shows a parallelogram. The dashed segments $AA'$ and $BB'$ are both the vector $\vec v$, so they are equal and parallel.

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Apply a translation by vector $\vec{v} = (6, 2)$ to the triangle with vertices $V_1(0, 0)$, $V_2(2, 0)$ and $V_3(1, 3)$. 1. Write the coordinates of the new vertices. 2.…

Apply a translation by vector $\vec{v} = (6, 2)$ to the triangle with vertices $V_1(0, 0)$, $V_2(2, 0)$ and $V_3(1, 3)$.

  1. Write the coordinates of the new vertices.

  2. How does the area of the new triangle compare to the original? Justify your answer.

Solve
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Consider the quadrilateral $ABCD$ whose vertices are $A(1, 1)$, $B(4, 1)$, $C(5, 3)$ and $D(2, 3)$. a) Apply a translation by vector $\vec{t} = (3, -4)$ and write the…

Consider the quadrilateral $ABCD$ whose vertices are $A(1, 1)$, $B(4, 1)$, $C(5, 3)$ and $D(2, 3)$.

  1. a) Apply a translation by vector $\vec{t} = (3, -4)$ and write the coordinates of the image figure $A'B'C'D'$.
  2. b) Calculate the area of the original quadrilateral and check if the translation has modified its value. Justify your answer based on the properties of isometries.
Solve
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Given the points $A(-2, 3)$ and $B(4, 7)$, a translation $T_1$ by vector $\vec{u} = (k, 2k)$ is applied to them. After this movement, the point $A$ is transformed into…

Given the points $A(-2, 3)$ and $B(4, 7)$, a translation $T_1$ by vector $\vec{u} = (k, 2k)$ is applied to them. After this movement, the point $A$ is transformed into $A'$. If we know that the modulus of the vector $\vec{AA'}$ is $10$ units and that $k > 0$:

  1. Find the value of $k$.

  2. Calculate the coordinates of $A'$ and $B'$.

  3. Show that the line segment $A'B'$ has the same length as the line segment $AB$. What property of translations is demonstrated by this?

Solve

Translating lines and circles

A line is made of points, so you can translate two of its points and draw the image. The image line is always parallel to the original, with the same slope. The translated line coincides with the original when the vector is parallel to the line.

Try it: the blue line is the original. Slide $h$ and $k$ and see when the orange image lands exactly on it.

A vertical line $x = c$ moves to $x = c + h$. Only the horizontal component matters. A horizontal line $y = c$ moves to $y = c + k$.

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On the Cartesian plane, we have a line $s$ that passes through the points $A(0, 2)$ and $B(2, 6)$. We apply a translation by vector $\vec{v} = (1, 3)$ to this line. a)…

On the Cartesian plane, we have a line $s$ that passes through the points $A(0, 2)$ and $B(2, 6)$. We apply a translation by vector $\vec{v} = (1, 3)$ to this line.

  1. a) Calculate the coordinates of the transformed points $A'$ and $B'$.
  2. b) Find the slope of the original line $s$ and of the translated line $s'$. What relationship do you observe between them?
  3. c) Are there any translation vectors that leave the line $s$ invariant (that is, the transformed line coincides with the original)? Give an example of one of these vectors.
Solve
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Consider the line $r$ whose equation is $y = 2x - 3$. We know that a translation leaves a line invariant (that is, the line is transformed into itself) if the…

Consider the line $r$ whose equation is $y = 2x - 3$. We know that a translation leaves a line invariant (that is, the line is transformed into itself) if the translation vector is parallel to that line.

  1. Find a translation vector $\vec{u} = (a, b)$ with modulus $\sqrt{20}$ that leaves the line $r$ invariant.

  2. If we apply that same vector $\vec{u}$ to the point $P(1, -1)$, which belongs to the line, what are the coordinates of the transformed point $P'$? Check analytically if $P'$ still belongs to the line $r$.

Solve
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In the design of a video game, a circular character with center at $C(x, y)$ and radius $R = 3$ must dodge an obstacle. The initial equation of its outline is…

In the design of a video game, a circular character with center at $C(x, y)$ and radius $R = 3$ must dodge an obstacle. The initial equation of its outline is $(x+4)^2 + (y-2)^2 = 9$.

The character is translated by the composition of two vectors: $\vec{u} = (7, 3)$ and $\vec{v} = (-2, 5)$.

  1. Determine the coordinates of the center $C$ before and after the composite translation.

  2. Write the equation of the circle in its final position.

  3. If the obstacle is a vertical wall located on the line $x = 5$, explain with reasoning whether the character collides with the wall after making the movement.

Wall x=5 X Y 0 −4 1 2 10 u(7,3) v(−2,5) w(5,8) C₁(−4,2) C₂(1,10) R=3
Solve

Repeating translations: friezes

A frieze is a pattern made by repeating one motif along a line, like the border along the top of a wall. You build it by applying the same translation again and again.

A triangle motif repeated three times along a horizontal line, each copy translated 3 units to the right of the previous one. ⟨3, 0⟩ 1st2nd3rd

The 2nd motif is one translation from the 1st, the 3rd is two translations from the 1st, and so on. Repeating $\vec w$ a total of $n$ times is the same as one translation by $n\vec w = \langle nw_1, nw_2\rangle$.

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A team of architects is designing a frieze for a new middle school. The basic motif is a letter "L" with vertices at $(0,0), (0,3), (1,3), (1,1), (2,1)$ and $(2,0)$. a)…

A team of architects is designing a frieze for a new middle school. The basic motif is a letter "L" with vertices at $(0,0), (0,3), (1,3), (1,1), (2,1)$ and $(2,0)$.

  1. a) Draw the motif on graph paper.
  2. b) To generate the frieze, they must successively apply the translation by vector $\vec{w} = (3, 0)$. Write the coordinates of the vertices of the second and third motifs of the frieze.
  3. c) What would be the translation vector needed to go directly from the first motif to the fifth?
0 1 2 3 6 9 12 15 1 2 3 M₄ M₅ M₁ M₂ M₃ w w v = 4w
Solve
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An architect designs a frieze by repeating a polygonal motif. The vertices of the basic motif are $A(0, 0)$, $B(2, 0)$, $C(3, 2)$ and $D(1, 2)$. To generate the frieze,…

An architect designs a frieze by repeating a polygonal motif. The vertices of the basic motif are $A(0, 0)$, $B(2, 0)$, $C(3, 2)$ and $D(1, 2)$. To generate the frieze, they successively apply the translation by vector $\vec{t} = (4, 0)$.

  1. Calculate the coordinates of the vertices of the third motif of the frieze (the one obtained after applying the translation twice consecutively to the original motif).

  2. If we want the frieze to be a composition of two different translations, $\vec{t_1}$ and $\vec{t_2}$, such that $\vec{t_1} + \vec{t_2} = (4, 0)$ and the first translation $\vec{t_1}$ displaces the motif upwards by $2$ units, what must the vector $\vec{t_1}$ and the vector $\vec{t_2}$ be?

Solve

Back to the start: "3 spaces right, 2 spaces up" is the vector $\vec v = \langle 3, 2\rangle$. It moves every point $(x, y)$ to $(x + 3,\ y + 2)$. The character traveled in a straight line a distance of $|\vec v| = \sqrt{3^2 + 2^2} = \sqrt{13} \approx 3.6$ spaces.

Summary

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