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Secondary 3 · Mathematics
Polynomials · Polynomials

Sum and Product of Polynomials

Before you start, make sure you know: Operations with monomials (Secondary Year 2 (first cycle))
Before you start, make sure you know: Properties of exponents (Secondary Year 1 (first cycle))

Wilkin helps out at his family's corner store and wants to calculate the area of a rectangular sign whose sides depend on $x$. Adding areas or finding the area of a bigger rectangle means working with polynomials. The rules are the same as with numbers; you just have to be careful to combine things of the same kind.

Monomials and polynomials: review

A monomial has a coefficient, a variable part, and a degree. In $-5x^3$: coefficient $-5$, variable part $x^3$, degree $3$. In $\frac{2}{3}ab^2$ the degree is $1+2=3$ (you add the exponents of all the variables). A number by itself, like $-7$, has degree $0$.

A polynomial is a sum of monomials. Like terms have the same variable part.

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Complete the following table, identifying the components of each monomial: | Monomial | Coefficient | Variable part | Degree | | :--- | :--- | :--- | :--- | | $-5x^3$ |…

Complete the following table, identifying the components of each monomial:

Monomial Coefficient Variable part Degree
$-5x^3$
$\frac{2}{3}ab^2$
$x^2y^2$
$-7$
Solve

Adding and subtracting polynomials

You add (or subtract) the like terms, that is, the terms that have the same variable part (the same letters with the same exponents). In a polynomial in $x$, they are the terms of the same degree. It helps to line them up in columns:

Addition of two polynomials in vertical form, lining up the monomials in columns by degree so that like coefficients can be added. degree 2degree 1degree 0 P(x) =4x²− 3x+ 5 Q(x) =x²+ 7x− 2 P + Q =5x²+ 4x+ 3 each column, one degree
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Given the polynomials $P(x) = 4x^2 - 3x + 5$ and $Q(x) = x^2 + 7x - 2$, perform the following operations by grouping like terms: a) $P(x) + Q(x)$ b) $P(x) - Q(x)$

Given the polynomials $P(x) = 4x^2 - 3x + 5$ and $Q(x) = x^2 + 7x - 2$, perform the following operations by grouping like terms:

  1. a) $P(x) + Q(x)$
  2. b) $P(x) - Q(x)$
Solve
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Find the polynomial expressing the perimeter of the following geometric figure (an L-block from a video game). Remember that the perimeter is the sum of all its sides.

Find the polynomial expressing the perimeter of the following geometric figure (an L-block from a video game). Remember that the perimeter is the sum of all its sides.

3x + 2 2x x + 1 x ? ?
Solve
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A streamer charges a fixed amount of $3\,000$ pesos per livestream and, in addition, receives $120$ pesos for each new subscription ($s$) and $30$ pesos for each…

A streamer charges a fixed amount of $3\,000$ pesos per livestream and, in addition, receives $120$ pesos for each new subscription ($s$) and $30$ pesos for each donation ($d$).

  1. Write the algebraic expression (polynomial) representing their total income in one day.

  2. If in a livestream they get $20$ subscriptions and $40$ donations, how much money have they earned in total?

Solve

Equality of polynomials

Two polynomials are equal when they have the same coefficients on the terms of the same degree. That is, if $ax^2+bx+c = dx^2+ex+f$ for all $x$, then $a=d$, $b=e$, and $c=f$.

Why? If two polynomials give the same value for every value of $x$, their difference is a polynomial that is always $0$, and that only happens if all its coefficients are $0$.

This is useful for finding unknown coefficients: you carry out the operations, put the terms in order, and compare the coefficients degree by degree.

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Given the polynomials $P(x) = 2x^2 - ax + 5$ and $Q(x) = bx^2 + 3x - c$, determine the values of the parameters $a$, $b$ and $c$ knowing that adding them yields the…

Given the polynomials $P(x) = 2x^2 - ax + 5$ and $Q(x) = bx^2 + 3x - c$, determine the values of the parameters $a$, $b$ and $c$ knowing that adding them yields the identity polynomial $S(x) = 5x^2 + x + 2$. Justify your answer by comparing the coefficients of the terms of the same degree.

Solve

Multiplying polynomials

Monomial times monomial: you multiply the coefficients and the variable parts (adding the exponents of the same variable): $(3x^2)\times(-4x^3) = -12x^5$.

Polynomial times polynomial: each term of the first multiplies every term of the second (distributive property). A rectangle shows this very well:

Geometric representation of polynomial multiplication using the area of a rectangle broken into four partial areas. 2x+3 x+1 2x²3x 2x3 (2x + 3)(x + 1) = 2x² + 3x + 2x + 3 = 2x² + 5x + 3 4 rectangles = 4 products
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Perform the following multiplications of monomials, applying index laws: a) $(3x^2) \times (4x^3) =$ b) $(-2a^2b) \times (5ab^3) =$ c) $(\frac{1}{2}x) \times (6x^5) =$

Perform the following multiplications of monomials, applying index laws:

  1. a) $(3x^2) \times (4x^3) =$
  2. b) $(-2a^2b) \times (5ab^3) =$
  3. c) $(\frac{1}{2}x) \times (6x^5) =$
Solve
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Apply the distributive property to calculate the area of the following rectangle, expressing the result as a polynomial:

Apply the distributive property to calculate the area of the following rectangle, expressing the result as a polynomial:

Area = ? 2x² + 5 3x
Solve
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Simplify the following polynomial expressions combining addition, subtraction and simple multiplication: a) $3 \times (x^2 - 2x + 1) + (4x - 5) =$ b)…

Simplify the following polynomial expressions combining addition, subtraction and simple multiplication:

  1. a) $3 \times (x^2 - 2x + 1) + (4x - 5) =$
  2. b) $x \times (x + 3) - (x^2 - 2) =$
Solve
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In a clothing store, the price of a hoodie is given by the polynomial $P(x) = 120x^2 + 600$, where $x$ is a logistics variable. If we buy $3x$ hoodies: 1. What is the…

In a clothing store, the price of a hoodie is given by the polynomial $P(x) = 120x^2 + 600$, where $x$ is a logistics variable. If we buy $3x$ hoodies:

  1. What is the polynomial that expresses the total cost of the purchase?

  2. If for a value of $x=2$, the price of one hoodie is in pesos, how much will the $3x$ hoodies cost for that same value?

Solve
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Given the polynomials $P(x) = 3x^2 - 5x + 2$ and $Q(x) = -x^2 + 2x - 7$, perform the following combined operations and simplify the resulting polynomial: a)…

Given the polynomials $P(x) = 3x^2 - 5x + 2$ and $Q(x) = -x^2 + 2x - 7$, perform the following combined operations and simplify the resulting polynomial:

  1. a) $2 \times P(x) + 3 \times Q(x)$
  2. b) $P(x) - [Q(x) + (x^2 - 1)]$
  3. c) $3x \times Q(x) + 5x^2$
Solve
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Apply the distributive property to multiply the following polynomials and collect like terms: a) $(2x - 3) \times (x^2 - 4x + 1)$ b) $(x^2 + 2) \times (x^2 - 2)$ c)…

Apply the distributive property to multiply the following polynomials and collect like terms:

  1. a) $(2x - 3) \times (x^2 - 4x + 1)$
  2. b) $(x^2 + 2) \times (x^2 - 2)$
  3. c) $-(x - 5) \times (2x + 3) + 2x^2$
Solve
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A company that manufactures tablets has designed a new model whose screen has the dimensions shown in the following figure. The outer border (bezel) has a constant width…

A company that manufactures tablets has designed a new model whose screen has the dimensions shown in the following figure. The outer border (bezel) has a constant width of $2$ cm on all sides.

SCREEN 3x + 5 2x 2 2 2 2
  1. a) Express the total area of the tablet (including the bezel) using a polynomial.
  2. b) Determine the polynomial representing the area of the screen alone (shaded area).
  3. c) Calculate the polynomial representing the area of the tablet's bezel.
Solve
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In the "AppZ" app store, the monthly revenue from selling a premium subscription is given by the polynomial $I(x) = 10x^2 + 50x$, where $x$ is the number of months since…

In the "AppZ" app store, the monthly revenue from selling a premium subscription is given by the polynomial $I(x) = 10x^2 + 50x$, where $x$ is the number of months since launch. On the other hand, maintenance costs are expressed as $G(x) = 2x^2 - 10x + 100$.

  1. a) Find the polynomial $B(x)$ that represents the company's net profits ($Beneficio = Ingresos - Gastos$).
  2. b) If the company decides to invest an extra amount in advertising equal to the product of $(x + 5) \times (x - 2)$, which is an additional cost, what would be the new total profit polynomial?
Solve
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Find the perimetre of the following geometric figure in terms of the variable $x$, expressing the result as a simplified polynomial.

Find the perimetre of the following geometric figure in terms of the variable $x$, expressing the result as a simplified polynomial.

x² + 5 2x x + 1 3x x² − x + 4 5x
Solve
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At a music festival, total revenue depends on the number of season tickets sold, represented by the variable $x$. The following polynomial functions have been…

At a music festival, total revenue depends on the number of season tickets sold, represented by the variable $x$. The following polynomial functions have been determined:

  • Ticket revenue: $I(x) = 3x^2 + 50x - 100$

  • Logistics and security expenses: $G(x) = 2x^2 - 15x + 500$

  • Marketing expenses: $M(x) = 10x + 1200$

If the net profit of the festival is calculated by subtracting all expenses from the revenue, find the simplified polynomial $B(x)$ that represents the profit. Once obtained, calculate the actual profit if $x = 100$ season tickets are sold.

Solve
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An architecture firm designs a rectangular town square containing a central circular fountain and a landscaped garden area. The total area of the square is defined by…

An architecture firm designs a rectangular town square containing a central circular fountain and a landscaped garden area. The total area of the square is defined by the product of its base $b(x) = 3x + 5$ and its height $h(x) = 2x - 1$. If the area of the fountain is given by the polynomial $F(x) = x^2 + 2x + 1$, find the polynomial that represents the area of the garden area (the remaining space of the square).

b(x) = 3x + 5 h(x) = 2x - 1 Fountain F(x) = x² + 2x + 1 Garden area A(x) = ?
Solve
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Work out the following combined operation and simplify the result as far as possible, ordering the polynomial in descending order of degree: $$(2x^2 - 3) \times (x^2 +…

Work out the following combined operation and simplify the result as far as possible, ordering the polynomial in descending order of degree:

$$(2x^2 - 3) \times (x^2 + 5x - 1) - [(x^2 - 2)^2 + 6x^3]$$

Pay special attention to expanding the algebraic identity and the negative sign affecting the square bracket.

Solve
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A courier company uses boxes whose dimensions (in cm) are in arithmetic progression and depend on a variable $x$: Width: $x - 2$ Length: $x + 1$ Height: $x + 4$ Find the…

A courier company uses boxes whose dimensions (in cm) are in arithmetic progression and depend on a variable $x$:

  • Width: $x - 2$

  • Length: $x + 1$

  • Height: $x + 4$

Find the polynomial $V(x)$ expressing the volume of the box. Then, find the polynomial $S(x)$ representing the total surface area of the six faces of the box. Simplify both expressions.

x + 1 Length x + 4 Height x - 2 Width
Solve
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Find the quadratic polynomial $P(x)$ such that it satisfies the following three conditions simultaneously: 1. Its leading coefficient is $3$. 2. It has no constant term.…

Find the quadratic polynomial $P(x)$ such that it satisfies the following three conditions simultaneously:

  1. Its leading coefficient is $3$.

  2. It has no constant term.

  3. When multiplied by the binomial $(x - 2)$, the coefficient of the degree $2$ term of the resulting product is equal to $-4$.

Solve

Degree in operations

When multiplying, the degrees add: $\text{gr}(A\cdot B)=\text{gr}(A)+\text{gr}(B)$. When adding, the degree is at most the larger of the two: $\text{gr}(A+B)\le \max(\text{gr}A,\text{gr}B)$. It can go down if the leading terms cancel, for example $(x^2+1)+(-x^2+3)=4$.

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Consider any two polynomials, $A(x)$ of degree $n$ and $B(x)$ of degree $m$. If we know that the degree of the product $A(x) \times B(x)$ is $7$ and that the degree of…

Consider any two polynomials, $A(x)$ of degree $n$ and $B(x)$ of degree $m$. If we know that the degree of the product $A(x) \times B(x)$ is $7$ and that the degree of the expression $(A(x) + B(x))^2$ is $8$, what are the individual degrees of $A(x)$ and $B(x)$? Reason your answer based on the properties of the degree of the sum and product of polynomials.

Solve

Common factor

This is the distributive property in reverse: if all the terms have something in common, you take it out in front, multiplying a set of parentheses.

$$6x^3 - 9x^2 + 3x = 3x\,(2x^2 - 3x + 1)$$ Diagram of taking out a common factor, showing how the term 3x is pulled out of each term to the front of the parentheses. 3x·2x² − 3x·3x + 3x·1 = 3x (2x² − 3x + 1) GCF of the coefficients and variables with the smallest exponent

Why does it work? Because applying the distributive property to $3x(2x^2-3x+1)$ gives back the original expression.

Common factor by grouping terms

Sometimes there is no common factor to all the terms, but there is one within groups of them. You group the terms and take out a common factor in each group; if the same parentheses are left, you take them out as a common factor. It works because of the distributive property: $a(x+y)+b(x+y)=(a+b)(x+y)$.

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Factorise the following algebraic expressions by taking out the common factor to write them as the product of a monomial and a polynomial: a) $15x^4 - 10x^3 + 5x^2$ b)…

Factorise the following algebraic expressions by taking out the common factor to write them as the product of a monomial and a polynomial:

  1. a) $15x^4 - 10x^3 + 5x^2$
  2. b) $3a^2b - 6ab^2 + 9ab$
  3. c) $2x(x+1) - 3(x+1)$
Solve

Special products

Some products come up so often that it pays to know them by heart. Their diagram explains where they come from:

Change $a$ and $b$ and see how the area of the big square is divided up:

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Calculate the resulting polynomial of the following expression using standard algebraic identities (square of a sum, square of a difference, and product of a sum and a…

Calculate the resulting polynomial of the following expression using standard algebraic identities (square of a sum, square of a difference, and product of a sum and a difference):

$A(x) = (2x + 3)^2 - (2x - 3)^2 + (x + 4) \times (x - 4)$

Simplify the final result as far as possible.

Solve
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Determine the value of the coefficient $k$ so that the following equality between polynomials holds true: $(x + 3) \times (2x - 5) = 2x^2 + kx - 15$ Once $k$ is found,…

Determine the value of the coefficient $k$ so that the following equality between polynomials holds true:

$(x + 3) \times (2x - 5) = 2x^2 + kx - 15$

Once $k$ is found, work out the product $(x + 3) \times (2x - 5) \times (x + 1)$ and write the resulting polynomial in descending order of degree.

Solve
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Expand and simplify the following expression involving three different variables ($x$, $y$, $z$). These types of expressions are common in physics formulae and data…

Expand and simplify the following expression involving three different variables ($x$, $y$, $z$). These types of expressions are common in physics formulae and data models:

$$(x + y - z) \times (x - y + z) + (y + z)^2 - z^2$$

Represent the final result as a simplified polynomial. What do you notice regarding the cross terms (such as $xy$ or $xz$)?

Solve

Factoring by cases

Factoring means writing a polynomial as a product. Special products, read in reverse, give the cases:

Case Form Factorization
Difference of squares $a^2-b^2$ $(a+b)(a-b)$
Perfect square trinomial $a^2\pm 2ab+b^2$ $(a\pm b)^2$
Trinomial $x^2+bx+c$ $x^2+(m+n)x+mn$ $(x+m)(x+n)$
Sum of cubes $a^3+b^3$ $(a+b)(a^2-ab+b^2)$
Difference of cubes $a^3-b^3$ $(a-b)(a^2+ab+b^2)$

Always start by looking for a common factor.

The trinomial $x^2+bx+c$

We look for two numbers $m$ and $n$ with $m\cdot n=c$ and $m+n=b$. There are two ways to justify and write it.

By grouping terms: you split the middle term into $mx+nx$ and group.

Completing the square: you add and subtract $\left(\frac{b}{2}\right)^2$ to form a perfect square trinomial and then a difference of squares.

Combined cases

Often you have to apply two or more cases in a row: first the common factor and then whatever is left. At the end, check that each factor can't be broken down any further.

Summary

Factoring case Form Result
a) Common factor $ax+ay$ $a(x+y)$
b) Common factor by grouping $ax+ay+bx+by$ $(x+y)(a+b)$
c) Difference of squares $a^2-b^2$ $(a+b)(a-b)$
d) Perfect square trinomial $a^2\pm2ab+b^2$ $(a\pm b)^2$
e) Trinomial $x^2+bx+c$ (grouping or completing the square) $x^2+(m+n)x+mn$ $(x+m)(x+n)$
g) Sum of cubes $a^3+b^3$ $(a+b)(a^2-ab+b^2)$
h) Difference of cubes $a^3-b^3$ $(a-b)(a^2+ab+b^2)$
i) Degree higher than two $x^3+\dots$ rational zeros, Descartes' rule of signs, and synthetic division (see "Division of Polynomials")

Back to the beginning: Wilkin's sign, with sides $(2x+3)$ and $(x+1)$, has area $2x^2+5x+3$.

See all the exercises in this section