Algebra 1 : How to factor a variable

Study concepts, example questions & explanations for Algebra 1

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Example Questions

Example Question #71 : Intermediate Single Variable Algebra

Two consecutive odd numbers have a product of 195. What is the sum of the two numbers?

Possible Answers:

\displaystyle 28

\displaystyle 31

\displaystyle 32

\displaystyle 29

Correct answer:

\displaystyle 28

Explanation:

You can set the two numbers to equal variables, so that you can set up the algebra in this problem. The first odd number can be defined as \displaystyle x and the second odd number, since the two numbers are consecutive, will be \displaystyle x+2.

This allows you to set up the following equation to include the given product of 195:

\displaystyle x(x+2)=195

\displaystyle x^2 + 2x = 195

Next you can subtract 195 to the left and set the equation equal to 0, which allows you to solve for \displaystyle x:

\displaystyle x^2+2x-195=0

You can factor this quadratic equation by determining which factors of 195 add up to 2. Keep in mind they will need to have opposite signs to result in a product of negative 195:

\displaystyle (x \ \ \ \ \ (x \ \ \ \ \ \) = 0\)

\displaystyle (x -13)(x +15) = 0

Set each binomial equal to 0 and solve for \displaystyle x. For the purpose of this problem, you'll only make use of the positive value for \displaystyle x:

\displaystyle x-13 = 0 \ \ \ \ \ \ x +15 = 0

\displaystyle x = 13

Now that you have solved for \displaystyle x, you know the two consecutive odd numbers are 13 and 15. You solve for the answer by finding the sum of these two numbers:

\displaystyle 13+15=28

Example Question #72 : Intermediate Single Variable Algebra

Factor:

\displaystyle x^2+3x

Possible Answers:

\displaystyle x(x+3)

\displaystyle 3(x^2+x)

\displaystyle (x^2)(3x)

\displaystyle x(x)(3)

Correct answer:

\displaystyle x(x+3)

Explanation:

The common factor here is \displaystyle x. Pull this out of both terms to simplify:

\displaystyle \frac{x(x^2+3x)}{x}=x(\frac{x^2}{x}+\frac{3x}{x})=x(x+3)

Example Question #12 : How To Factor A Variable

Factor the following polynomial: \displaystyle x^2-2x-35.

Possible Answers:

\displaystyle (x-1)(x+35)

\displaystyle (x+5)(x-7)

\displaystyle (x-5)(x-7)

\displaystyle (x+5)(x+7)

\displaystyle (x-35)(x-1)

Correct answer:

\displaystyle (x+5)(x-7)

Explanation:

Because the \displaystyle x^2 term doesn’t have a coefficient, you want to begin by looking at the \displaystyle c term (\displaystyle ax^2+bx+c) of the polynomial: \displaystyle -35.  Find the factors of \displaystyle -35 that when added together equal the second coefficient (the \displaystyle b term) of the polynomial. 

There are only four factors of \displaystyle 35: \displaystyle 1, 5, 7, 35, and only two of those factors, \displaystyle 5, 7, can be manipulated to equal \displaystyle -2 when added together and manipulated to equal \displaystyle -35 when multiplied together: \displaystyle 5, -7 (i.e.,\displaystyle 5-7=-2). 

Example Question #13 : How To Factor A Variable

Factor the following polynomial: \displaystyle x^2+13x+30.

Possible Answers:

\displaystyle (x-10)(x+3)

\displaystyle (x-10)(x-3)

\displaystyle (x+5)(x+6)

\displaystyle (x+10)(x+3)

\displaystyle (x-5)(x-6)

Correct answer:

\displaystyle (x+10)(x+3)

Explanation:

Because the \displaystyle x^2 term doesn’t have a coefficient, you want to begin by looking at the \displaystyle c term (\displaystyle ax^2+bx+c) of the polynomial: \displaystyle 30

Find the factors of \displaystyle 30 that when added together equal the second coefficient (the \displaystyle b term) of the polynomial: \displaystyle 13

There are seven factors of \displaystyle 30\displaystyle 1, 2, 3, 5, 6, 10, 15, and only two of those factors, \displaystyle 3, 10, can be manipulated to equal \displaystyle 13 when added together and manipulated to equal \displaystyle 30 when multiplied together: \displaystyle 3, 10 

\displaystyle 3+10=13, 3\times10=30

Example Question #95 : Polynomials

Solve for \displaystyle x when \displaystyle x\neq-5\displaystyle \frac{x^2+2x-15}{x+5}=10

Possible Answers:

\displaystyle x=-5

\displaystyle x=5

\displaystyle x=7

\displaystyle x=15

\displaystyle x=13

Correct answer:

\displaystyle x=13

Explanation:

First, factor the numerator: \displaystyle (x+5)(x-3).  

Now your expression looks like 

\displaystyle \frac{(x+5)(x-3)}{x+5}

Second, cancel the "like" terms - \displaystyle (x+5) - which leaves us with \displaystyle x-3=10.  

Third, solve for \displaystyle x, which leaves you with \displaystyle x=13

Example Question #421 : Polynomials

Factor the following polynomial: \displaystyle 2x^2-5x-3.

Possible Answers:

\displaystyle (2x+1)(x-3)

\displaystyle (2x-1)(x+3)

\displaystyle (2x+3)(x+1)

\displaystyle (2x+1)(x+3)

\displaystyle (2x+3)(x-1)

Correct answer:

\displaystyle (2x+1)(x-3)

Explanation:

Because the \displaystyle x^2 term has a coefficient, you begin by multiplying the \displaystyle a and the \displaystyle c terms (\displaystyle ax^2+bx+c) together: \displaystyle 2\times-3=-6

Find the factors of \displaystyle -6 that when added together equal the second coefficient (the \displaystyle b term) of the polynomial: \displaystyle -5

There are four factors of \displaystyle 6\displaystyle 1, 2, 3, 6, and only two of those factors, \displaystyle 1, 6, can be manipulated to equal \displaystyle -5 when added together and manipulated to equal \displaystyle -6 when multiplied together: \displaystyle 1, -6 

\displaystyle 1+-6=-5, 1\times-6=-6

Example Question #12 : How To Factor A Variable

Factor:  \displaystyle x^6+2x^3+2x

Possible Answers:

\displaystyle x(x^5+2x^2+2)

\displaystyle x(6x^5+2x^2+2)

\displaystyle 6x(x^5+2x+\frac{1}{3})

\displaystyle \frac{1}{x^6}(x^{-6}+2x^{-2}+2x^{-5})

\displaystyle x^3(x^3+4)

Correct answer:

\displaystyle x(x^5+2x^2+2)

Explanation:

For each term in this expression, we will notice that each shares a variable of \displaystyle x.  This can be pulled out as a common factor.

\displaystyle x^6+2x^3+2x = x(x^5+2x^2+2)

There are no more common factors, and this is the reduced form.

The answer is:  \displaystyle x(x^5+2x^2+2)

Example Question #13 : How To Factor A Variable

Factor:  \displaystyle x^6+2x^3-3x

Possible Answers:

\displaystyle x^3(x^3-8)

\displaystyle \frac{1}{x^6}(x^{-6}+2x^{-2}-3x^{-5})

\displaystyle 6x(x^5+2x-\frac{1}{18})

\displaystyle x(6x^5+2x^2-2)

\displaystyle x(x^5+2x^2-3)

Correct answer:

\displaystyle x(x^5+2x^2-3)

Explanation:

For each term in this expression, we will notice that each shares a variable of \displaystyle x.  This can be pulled out as a common factor.

\displaystyle x^6+2x^3-3x = x(x^5+2x^2-3)

There are no more common factors, and this is the reduced form.

The answer is:  \displaystyle x(x^5+2x^2-3)

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