Algebraic Expressions
A family music plan on your phone costs $x$ pesos a month, and three friends are going to split it. You don't know exactly how much it costs, but you already know the calculation you need to do: $\dfrac{x}{3}$. That is what algebra is: writing the calculation before you know the numbers.
Variables and Translating Phrases
Each key word turns into an operation. When the phrase has several steps, translate from the inside out, like following a recipe.
| Everyday language | Algebraic language |
|---|---|
| Twice a number plus 5 | $2x + 5$ |
| Twice (a number plus 5) | $2(x + 5)$ |
| Half a number minus 3 | $\dfrac{x}{2} - 3$ |
| A 5-peso discount coupon on the price $x$ | $x - 5$ |
In an online video game store, the price of a monthly subscription is $x$ pesos. Translate the following situations into algebraic expressions: a) The cost of three…
In an online video game store, the price of a monthly subscription is $x$ pesos. Translate the following situations into algebraic expressions:
- a) The cost of three monthly subscriptions.
- b) The price of a subscription after applying a discount coupon of $100$ pesos.
- c) What a group of friends pays for a monthly subscription plus a game costing $500$ pesos.
- d) Double the price of a subscription increased by $200$ pesos.
A municipal sports center has a rectangular basketball court. If the length of the court is $y$ meters and its width is half the length, write the polynomial that…
A municipal sports center has a rectangular basketball court. If the length of the court is $y$ meters and its width is half the length, write the polynomial that represents the area of the court in terms of $y$.
In a comic shop, the price of a monthly subscription is $x$ pesos. For each additional comic you buy, you are charged $y$ pesos, but if you buy more than five, a…
In a comic shop, the price of a monthly subscription is $x$ pesos. For each additional comic you buy, you are charged $y$ pesos, but if you buy more than five, a discount of $60$ pesos is applied to the total. Write the algebraic expression that represents the monthly expenditure of a customer who has bought $7$ additional comics.
The Numerical Value
This also works for finding values that make a polynomial equal zero. If $x = 2$ must give $0$ in $x^3 - kx + 6$, we substitute: $8 - 2k + 6 = 0$, so $14 = 2k$, which means $k = 7$.
Calculate the numerical value of the following algebraic expressions for the given values: a) $5x - 3$ for $x = 4$ b) $x^{2} + 2x + 1$ for $x = -2$ c) $2(a + b)$ for…
Calculate the numerical value of the following algebraic expressions for the given values:
- a) $5x - 3$ for $x = 4$
- b) $x^{2} + 2x + 1$ for $x = -2$
- c) $2(a + b)$ for $a = 3$ and $b = 5$
- d) $\frac{10 - x}{2}$ for $x = 6$
Find the numerical value of the polynomial $P(x, y) = 3x^2y - 5xy + 2$ for the given values of the variables: a) $x = 2, y = -1$ b) $x = 0, y = 10$ c) $x = -2, y = -2$
Find the numerical value of the polynomial $P(x, y) = 3x^2y - 5xy + 2$ for the given values of the variables:
- a) $x = 2, y = -1$
- b) $x = 0, y = 10$
- c) $x = -2, y = -2$
Consider the polynomial $P(x) = 2x^3 - kx^2 + 4x - 12$. 1. Determine the value of the coefficient $k$ knowing that the numerical value of the polynomial for $x = 2$ is…
Consider the polynomial $P(x) = 2x^3 - kx^2 + 4x - 12$.
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Determine the value of the coefficient $k$ knowing that the numerical value of the polynomial for $x = 2$ is equal to zero ($x = 2$ is a root of the polynomial).
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Once $k$ has been found, calculate the numerical value of $P(x)$ for $x = -1$.
Monomials, Polynomials, and Like Terms
A monomial is a single term: a number (the coefficient) times letters with exponents (the variable part). Its degree is the sum of the exponents of the variable part.
| Monomial | Coefficient | Variable part | Degree |
|---|---|---|---|
| $7x^2$ | $7$ | $x^2$ | $2$ |
| $-5ab^3$ | $-5$ | $ab^3$ | $1 + 3 = 4$ |
| $x^4y$ | $1$ | $x^4y$ | $5$ |
A polynomial is a sum of monomials. It is called a binomial if it has 2 terms and a trinomial if it has 3. The degree of the polynomial is the highest degree among its terms: $4x^3 - 5x + 2$ is a trinomial of degree $3$.
Two terms are like terms if they have exactly the same variable part. Only they can be added or subtracted: you add the coefficients and the variable part stays the same. For example, $7a^2 + 2a^2 = 9a^2$, but $7a^2 + 2a$ cannot be simplified. It's like counting objects: $3$ cakes $+$ $2$ cakes $= 5$ cakes, but $3$ cakes $+$ $2$ sodas isn't $5$ of anything.
Identify the parts of the following monomials by completing the information for each: a) $7x^{2}$ b) $-5ab^{3}$ c) $x^{4}y$ d) $\frac{3}{4}z^{2}$ For each one, state the…
Identify the parts of the following monomials by completing the information for each:
- a) $7x^{2}$
- b) $-5ab^{3}$
- c) $x^{4}y$
- d) $\frac{3}{4}z^{2}$
For each one, state the Coefficient, Literal part and Degree.
Classify the following algebraic expressions, indicating whether they are monomials, binomials or trinomials. In the case of polynomials (binomials and trinomials), also…
Classify the following algebraic expressions, indicating whether they are monomials, binomials or trinomials. In the case of polynomials (binomials and trinomials), also state their degree.
- a) $4x^{3} - 5x + 2$
- b) $-7ab^{2}$
- c) $x^{2} + 10$
- d) $3y^{4} - 2y^{2}$
Simplify the following algebraic expressions by adding or subtracting like terms: a) $3x + 5x - 2x$ b) $7a^{2} - 3a + 2a^{2} + 5a$ c) $4xy + 2x - xy + 3x$ d)…
Simplify the following algebraic expressions by adding or subtracting like terms:
- a) $3x + 5x - 2x$
- b) $7a^{2} - 3a + 2a^{2} + 5a$
- c) $4xy + 2x - xy + 3x$
- d) $10n - 5 - 3n + 8$
Perimeters and Areas with Letters
When the measurements of a figure are algebraic expressions, the perimeter is the sum of all the sides and the area is built with the usual formulas. Then you simplify the like terms.
For composite figures, add or subtract areas. For example, a $2$ cm frame around a screen of $x$ by $(x + 4)$ makes the total rectangle $2 + x + 2 = x + 4$ wide and $x + 4 + 4 = x + 8$ long. The area of the frame is the total area minus the area of the screen (in the next section you will learn how to multiply those binomials).
We are designing a new tablet whose screen is rectangular. The base measures $x$ centimeters and the height is $5$ centimeters less than the base. Write an algebraic…
We are designing a new tablet whose screen is rectangular. The base measures $x$ centimeters and the height is $5$ centimeters less than the base. Write an algebraic expression for the perimeter of the screen and simplify it.
Find the algebraic expression that represents the area of the following geometric figure in terms of $x$. Simplify the result by collecting like terms.
Find the algebraic expression that represents the area of the following geometric figure in terms of $x$. Simplify the result by collecting like terms.
Patterns and the General Term
When a figure always grows by the same rule, you can describe any position $n$ at once with an expression: the general term $a_n$.
With $n = 1$ there are $2$ dots; with $n = 2$, $4$; with $n = 3$, $6$. Each position adds $2$, so $a_n = 2n$.
If the difference between terms is constant ($d$), the general term is $a_n = dn + (a_1 - d)$. For example, $5, 8, 11, 14, \ldots$ goes up by $3$ each time: $a_n = 3n + (5 - 3) = 3n + 2$.
If the difference is not constant, look at the differences of the differences. If these second differences are constant, the general term has an $n^2$.
Observe the following sequence of patterns made with dots and determine the algebraic expression for the general term $a_{n}$ (where $n$ is the position of the pattern).…
Observe the following sequence of patterns made with dots and determine the algebraic expression for the general term $a_{n}$ (where $n$ is the position of the pattern). How many dots will the pattern in position $n=50$ have?
A digital artist is creating a pixel mosaic that grows following a certain pattern. In stage $n=1$ they use 3 pixels, in stage $n=2$ they use 8 pixels, in stage $n=3$…
A digital artist is creating a pixel mosaic that grows following a certain pattern. In stage $n=1$ they use 3 pixels, in stage $n=2$ they use 8 pixels, in stage $n=3$ they use 15 pixels, and so on.
Look at the visual pattern and complete the following tasks:
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Find the algebraic expression (nth term) that determines the number of pixels required for any stage $n$.
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If the digital canvas has a limit of $1000$ pixels, could the artist complete stage $n=30$? Justify your answer by calculating the numerical value.
Adding and Subtracting Polynomials
To add polynomials, you write one after the other and simplify the like terms. To subtract, you change the sign of every term of the second one (it's multiplying by $-1$).
You can also multiply a polynomial by a number before adding: $2A + 3B$ means multiplying each term of $A$ by $2$ and of $B$ by $3$, and then simplifying. The same happens with percents: a price with $16\,\%$ VAT (IVA) is $1.16$ times the base price. If a scooter app charges $B$ pesos as a base fee and $4$ pesos per minute $m$, with $16\,\%$ VAT (IVA) the total is $C = 1.16(B + 4m) = 1.16B + 4.64m$.
Given the polynomials $A(x) = 4x^3 - 6x^2 + 5x$ and $B(x) = -2x^3 + 8x^2 - 7$, perform the following operations and write the resulting polynomial in descending order of…
Given the polynomials $A(x) = 4x^3 - 6x^2 + 5x$ and $B(x) = -2x^3 + 8x^2 - 7$, perform the following operations and write the resulting polynomial in descending order of degree:
- a) $A(x) + B(x)$
- b) $A(x) - B(x)$
- c) $2 \times A(x) + 3 \times B(x)$
An electric scooter rental company charges a base fee of $B$ pesos for unlocking and $3$ pesos per minute of use ($m$). In addition, if the user travels more than $5$…
An electric scooter rental company charges a base fee of $B$ pesos for unlocking and $3$ pesos per minute of use ($m$). In addition, if the user travels more than $5$ kilometers, a safety surcharge of $S$ pesos is applied. A tax of $21\%$ must be applied to the sum of these items.
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Write the algebraic expression for the total cost $C$ of a trip if the user exceeds a distance of $5$ km.
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Simplify the previous expression by performing any possible operations.
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If the base fee is $20$ pesos and the safety surcharge is $40$ pesos, how much will a person pay who uses the scooter for $20$ minutes and travels $6$ km?
Multiplying Monomials and Polynomials
To multiply with letters we use the rules of exponents:
The coefficients are multiplied together and equal letters add their exponents: $3x \cdot 2x^2 = 6x^3$. To divide, you divide the coefficients and subtract the exponents: $\dfrac{12x^4}{3x} = 4x^3$.
To multiply a monomial by a polynomial, or two polynomials, you use the distributive property: each term of one multiplies each term of the other, and then the like terms are simplified.
This is useful for areas: if the length of a rectangle is $x + 8$ and the width is $x + 4$, the area is $(x+8)(x+4) = x^2 + 12x + 32$. Subtracting the screen ($x^2 + 4x$) leaves the frame: $8x + 32$.
Simplify the following algebraic expression as far as possible by operating with monomials and removing the brackets:…
Simplify the following algebraic expression as far as possible by operating with monomials and removing the brackets:
$3x \times (2x^2) - 4x^2 \times (x - 5) + \frac{12x^4}{3x}$
A surveillance drone flies over a rectangular plot whose dimensions are given by the polynomials $L(x) = x^2 - 3x + 5$ for the length and $A(x) = 2x + 1$ for the width.…
A surveillance drone flies over a rectangular plot whose dimensions are given by the polynomials $L(x) = x^2 - 3x + 5$ for the length and $A(x) = 2x + 1$ for the width. Obtain the polynomial that represents the total area of the plot.
The new model of a smartphone has a rectangular glass screen with dimensions of $x$ in width and $x+4$ in length. Around the screen there is a protective frame or bezel…
The new model of a smartphone has a rectangular glass screen with dimensions of $x$ in width and $x+4$ in length. Around the screen there is a protective frame or bezel with a uniform thickness of $2$ cm on all sides.
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Find the simplified polynomial that expresses the total area of the front of the phone (screen plus bezel).
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Find the simplified polynomial that expresses only the area of the bezel (the gray area).
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If the width of the screen $x$ is $6$ cm, what is the area of the bezel?
Special Products
Some products come up so often that it's worth memorizing them. They are called special products.
Special products are also useful for proofs. If we call two consecutive integers $n$ and $n + 1$, the difference of their squares is $(n+1)^2 - n^2 = n^2 + 2n + 1 - n^2 = 2n + 1$. This is $n + (n + 1)$: the sum of the two numbers. With $12$ and $13$: $169 - 144 = 25 = 12 + 13$. ✓
Use algebraic identities to expand the following expressions without multiplying step by step: a) $(3x + 5)^2$ b) $(2a - 4b)^2$ c) $(x^2 + 3) \times (x^2 - 3)$
Use algebraic identities to expand the following expressions without multiplying step by step:
- a) $(3x + 5)^2$
- b) $(2a - 4b)^2$
- c) $(x^2 + 3) \times (x^2 - 3)$
Prove algebraically that the difference between the squares of two consecutive integers is always equal to the sum of those numbers. Instructions:* 1. Call the first…
Prove algebraically that the difference between the squares of two consecutive integers is always equal to the sum of those numbers.
Instructions:
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Call the first number $n$ and the next number $n+1$.
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Write the expression for the difference of their squares: $(n+1)^2 - n^2$.
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Expand and simplify the expression.
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Check the result with the numbers $12$ and $13$.
Expand and simplify the following algebraic expression as far as possible using algebraic identities to collect like terms: $$(3x - 5)^2 - (3x + 5)(3x - 5) - 10(3 -…
Expand and simplify the following algebraic expression as far as possible using algebraic identities to collect like terms:
$$(3x - 5)^2 - (3x + 5)(3x - 5) - 10(3 - 3x)$$Show the process step by step, indicating which algebraic identity you have used in each case.
Common Factor and Simplification
Factoring out a common factor is the distributive property in reverse: we look for what is repeated in all the terms and write it outside a set of parentheses. You take the GCF of the coefficients and each letter with its lowest exponent.
With letters in geometry: the area of a ring is $\pi R^2 - \pi r^2 = \pi(R^2 - r^2)$.
Special products can also be read in reverse: $x^2 - 9 = (x+3)(x-3)$ and $x^2 + 6x + 9 = (x+3)^2$. This is how algebraic fractions are simplified:
Factorise the following algebraic expressions as far as possible by taking out the highest common factor: a) $15x^4 - 10x^3 + 5x^2$ b) $6a^2b - 9ab^2 + 3ab$ c)…
Factorise the following algebraic expressions as far as possible by taking out the highest common factor:
- a) $15x^4 - 10x^3 + 5x^2$
- b) $6a^2b - 9ab^2 + 3ab$
- c) $12x^2y^3 - 18x^3y^2$
A play area in a park is to be designed, consisting of a large circle with radius $R$. Inside this circle, a square sandbox will be installed whose side length is…
A play area in a park is to be designed, consisting of a large circle with radius $R$. Inside this circle, a square sandbox will be installed whose side length is exactly the radius $R$ of the circle. The rest of the circle will be covered with artificial grass.
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Write the simplified algebraic expression for the area of the artificial grass zone in terms of $R$. Use $\pi$ as a symbol.
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Factorize the resulting expression by taking out the common factor.
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If the radius $R$ is $10$ meters, calculate the grass area (use $\pi \approx 3.14$).
Simplify the following algebraic fraction by first taking out common factors and using algebraic identities in the numerator and the denominator: $$\frac{2x^3 - 8x}{x^2…
Simplify the following algebraic fraction by first taking out common factors and using algebraic identities in the numerator and the denominator:
$$\frac{2x^3 - 8x}{x^2 + 4x + 4}$$For what value of $x$ would this expression be undefined? (Hint: the denominator cannot be zero).
Back to the beginning: if the music plan costs $x = 180$ pesos a month, each friend pays $\dfrac{180}{3} = 60$ pesos. The expression $\dfrac{x}{3}$ works for any price.