ACT Math : How to factor an equation

Example Questions

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Example Question #481 : Algebra

Solve 8x2 – 2x – 15 = 0

x = -3/2 or 5/4

x = 3/2 or -5/4

x = -3/2 or -5/4

x = 3/2 or 5/4

x = 3/2 or -5/4

Explanation:

The equation is in standard form, so a = 8, b = -2, and c = -15.  We are looking for two factors that multiply to ac or -120 and add to b or -2.  The two factors are -12 and 10.

So you get (2x -3)(4x +5) = 0.  Set each factor equal to zero and solve.

Example Question #482 : Algebra

If , and , which of the following is a possible value of ?

-4

-6

-2

-12

-8

-12

Explanation:

The given expression is a quadratic equation; therefore, we can factor the equation

We will use the format of the standard quadratic equation:

Since , we know that the quadratic's roots will resemble the following:

We also know that one of those signs has to be negative, because our two last terms multiply to equal the variable  and  is negative in our quadratic. Now, we need to find two numbers that when multiplied together equal -24, and equal 10 when they are added together. Let's start by finding the factors of 24. The factors of 24 are: 24 and 1; 12 and 2; 8 and 3; and 6 and 4. Since one of those factors will be negative in our factored equation, we need to find the two factors whose difference is 10.

This means that the numbers in the factored equation are 12 and -2; thus, we may write the following:

.

By the zero multiplication rule, either portion of that equation can equal 0 for the result to be 0; thus, we have the following two expressions:

Subtract 12 from both sides of the equation:

Let's calculate the value of the variable in the second equation.

Add 2 to both sides of the equation.

Since we want a negative answer for our variable, the correct answer is:

Example Question #1 : How To Factor An Equation

If (x+ 2) / 2 = (x2 - 6x - 1) / 5, then what is the value of x?

4

-2

2

-3

3

-2

Explanation:

(x+ 2) / 2 = (x2 - 6x - 1) / 5. We first cross-multiply to get rid of the denominators on both sides.

5(x2 + 2) = 2(x2 - 6x - 1)

5x2 + 10 = 2x2 - 12x - 2 (Subtract 2x2, and add 12x and 2 to both sides.)

3x2 + 12x + 12 = 0 (Factor out 3 from the left side of the equation.)

3(x2 + 4x + 4) = 0 (Factor the equation, knowing that 2 + 2 = 4 and 2*2 = 4.)

3(x + 2)(x + 2) = 0

x + 2 = 0

x = -2

Example Question #2 : How To Factor An Equation

Which of the following is a factor of the polynomial x2 – 6x + 5?

x + 1

x – 5

x – 6

x – 8

x + 2

x – 5

Explanation:

Factor the polynomial by choosing values that when FOIL'ed will add to equal the middle coefficient, 3, and multiply to equal the constant, 1.

x2 – 6+ 5 = (x – 1)(x – 5)

Because only (x – 5) is one of the choices listed, we choose it.

Example Question #2 : How To Factor An Equation

7 times a number is 30 less than that same number squared. What is one possible value of the number?

Explanation:

Either:

or:

Example Question #4 : How To Factor An Equation

Which of the following is equivalent to ?

Explanation:

To determine the answer,  must be distrbuted,

. After multiplying the terms, the expression simplifies to .

Example Question #487 : Algebra

For what value of b is the equation b2 + 6b + 9 = 0 true?

3

5

0

3

3

Explanation:

Example Question #5 : How To Factor An Equation

What is the solution to:

1

2

6

4

0

4

Explanation:

First you want to factor the numerator from x– 6x + 8 to (x – 4)(x – 2)

Input the denominator (x – 4)(x – 2)/(x – 2) = (x – 4) = 0, so x = 4.

Example Question #489 : Algebra

What is the value of  where:

Explanation:

The question asks us to find the value of , because it is in a closed equation, we can simply put all of the whole numbers on one side of the equation, and all of the  containing numbers on the other side.

We utilize opposite operations to both sides by adding  to each side of the equation and get

Next, we subtract  from both sides, yielding

Then we divide both sides by  to get rid of that  on

Example Question #6 : How To Factor An Equation

Factor the following equation: