SAT Math : Factoring

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #1 : Variables

Factor the following variable

(x2 + 18x + 72)

Possible Answers:

(x – 6) (x – 12)

(x + 6) (x – 12)

(x + 18) (x + 72)

(x – 6) (x + 12)

(x + 6) (x + 12)

Correct answer:

(x + 6) (x + 12)

Explanation:

You need to find two numbers that multiply to give 72 and add up to give 18

easiest way: write the multiples of 72:

1, 72

2, 36

3, 24

4, 18

6, 12: these add up to 18

 (x + 6)(x + 12)

Example Question #1 : Factoring

Factor 9x2 + 12x + 4.

Possible Answers:

(3x + 2)(3x + 2)

(3x – 2)(3x – 2)

(9x + 4)(9x – 4)

(3x + 2)(3x – 2)

(9x + 4)(9x + 4)

Correct answer:

(3x + 2)(3x + 2)

Explanation:

Nothing common cancels at the beginning. To factor this, we need to find two numbers that multiply to 9 * 4 = 36 and sum to 12. 6 and 6 work.

So 9x2 + 12x + 4 = 9x2 + 6x + 6x + 4

Let's look at the first two terms and last two terms separately to begin with. 9x2 + 6x can be simplified to 3x(3x + 2) and 6x + 4 can be simplified into 2(3x + 2). Putting these together gets us 

9x2 + 12x + 4

= 9x2 + 6x + 6x + 4

= 3x(3x + 2) + 2(3x + 2) 

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

This is as far as we can factor. 

Example Question #1 : Factoring

If \dpi{100} \small \frac{x^{2}-9}{x+3}=5\(\displaystyle \dpi{100} \small \frac{x^{2}-9}{x+3}=5\) , and \dpi{100} \small x\neq -3\(\displaystyle \dpi{100} \small x\neq -3\) , what is the value of \dpi{100} \small x\(\displaystyle \dpi{100} \small x\)?

Possible Answers:

–8

–6

8

0

6

Correct answer:

8

Explanation:

The numerator on the left can be factored so the expression becomes \dpi{100} \small \frac{\left ( x+3 \right )\times \left ( x-3 \right )}{\left ( x+3 \right )}=5\(\displaystyle \dpi{100} \small \frac{\left ( x+3 \right )\times \left ( x-3 \right )}{\left ( x+3 \right )}=5\), which can be simplified to \dpi{100} \small \left ( x-3 \right )=5\(\displaystyle \dpi{100} \small \left ( x-3 \right )=5\)

Then you can solve for \dpi{100} \small x\(\displaystyle \dpi{100} \small x\) by adding 3 to both sides of the equation, so \dpi{100} \small x=8\(\displaystyle \dpi{100} \small x=8\)

Example Question #4 : Factoring

Solve for x:

\small x^2+3x+2=0\(\displaystyle \small x^2+3x+2=0\)

Possible Answers:

\dpi{100} \small x=-2\ or\ 1\(\displaystyle \dpi{100} \small x=-2\ or\ 1\)

\dpi{100} \small x=2\ or\ 1\(\displaystyle \dpi{100} \small x=2\ or\ 1\)

\dpi{100} \small x=-2\ or-1\(\displaystyle \dpi{100} \small x=-2\ or-1\)

\dpi{100} \small x=2\ or-1\(\displaystyle \dpi{100} \small x=2\ or-1\)

Correct answer:

\dpi{100} \small x=-2\ or-1\(\displaystyle \dpi{100} \small x=-2\ or-1\)

Explanation:

First, factor.

\small x^2+3x+2=(x+2)(x+1)=0\(\displaystyle \small x^2+3x+2=(x+2)(x+1)=0\)

Set each factor equal to 0

\small x+2=0; x=-2\(\displaystyle \small x+2=0; x=-2\)

\small x+1=0; x=-1\(\displaystyle \small x+1=0; x=-1\)

Therefore,

\dpi{100} \small x=-2\ or-1\(\displaystyle \dpi{100} \small x=-2\ or-1\)

Example Question #3 : Factoring Polynomials

When \(\displaystyle x^2-y^2-z^2+2yz\) is factored, it can be written in the form \(\displaystyle (ax + by + cz)(dx + ey + fz)\), where \(\displaystyle a\), \(\displaystyle b\), \(\displaystyle c\), \(\displaystyle d\), \(\displaystyle e\), and \(\displaystyle f\) are all integer constants, and \(\displaystyle a>0\).

What is the value of \(\displaystyle a + b + c + d + e + f\)?

Possible Answers:

\(\displaystyle -2\)

\(\displaystyle 2\)

\(\displaystyle -1\)

\(\displaystyle 0\)

\(\displaystyle 1\)

Correct answer:

\(\displaystyle 2\)

Explanation:

Let's try to factor x2 – y2 – z2 + 2yz.

Notice that the last three terms are very close to y2 + z2 – 2yz, which, if we rearranged them, would become y2 – 2yz+ z2. We could factor y2 – 2yz+ z2 as (y – z)2, using the general rule that p2 – 2pq + q2 = (p – q)2 .

So we want to rearrange the last three terms. Let's group them together first.

x2 + (–y2 – z2 + 2yz)

If we were to factor out a –1 from the last three terms, we would have the following:

x2 – (y2 + z2 – 2yz)

Now we can replace y2 + z2 – 2yz with (y – z)2.

x2 – (y – z)2

This expression is actually a differences of squares. In general, we can factor p2 – q2 as (p – q)(p + q). In this case, we can substitute x for p and (y – z) for q.

x2 – (y – z)= (x – (y – z))(x  + (y – z))

Now, let's distribute the negative one in the trinomial x – (y – z)

(x – (y – z))(x  + (y – z)) 

(x – y + z)(x + y – z)

The problem said that factoring x2 – y2 – z2 + 2yz would result in two polynomials in the form (ax + by + cz)(dx + ey + fz), where a, b, c, d, e, and f were all integers, and a > 0.

(x – y + z)(x + y – z) fits this form. This means that a = 1, b = –1, c = 1, d = 1, e = 1, and f = –1. The sum of all of these is 2.

The answer is 2. 

Example Question #2 : Factoring

Factor and simplify:

\frac{64y^{2} - 16}{8y + 4}\(\displaystyle \frac{64y^{2} - 16}{8y + 4}\)

Possible Answers:

8y-12\(\displaystyle 8y-12\)

8y\(\displaystyle 8y\)

8y-4\(\displaystyle 8y-4\)

-4\(\displaystyle -4\)

8y+4\(\displaystyle 8y+4\)

Correct answer:

8y-4\(\displaystyle 8y-4\)

Explanation:

64y^{2} - 16\(\displaystyle 64y^{2} - 16\) is a difference of squares.

The difference of squares formula is a^{2} - b^{2} = (a - b)(a + b)\(\displaystyle a^{2} - b^{2} = (a - b)(a + b)\).

Therefore, \frac{64y^{2} - 16}{8y + 4}\(\displaystyle \frac{64y^{2} - 16}{8y + 4}\) = \frac{(8y + 4)(8y - 4)}{8y + 4} = 8y - 4\(\displaystyle \frac{(8y + 4)(8y - 4)}{8y + 4} = 8y - 4\).

Example Question #2 : Factoring

Factor:

-12x^2+27\(\displaystyle -12x^2+27\)

Possible Answers:

-3(4x^{2}-9)\(\displaystyle -3(4x^{2}-9)\)

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

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

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

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

Correct answer:

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

Explanation:

We can first factor out -3\(\displaystyle -3\):

-3(4x^{2}-9)\(\displaystyle -3(4x^{2}-9)\)

This factors further because there is a difference of squares:

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

Example Question #2181 : Sat Mathematics

A group of scientists form a global collective of temperature and climate data. U.S. temperature measurements are in Fahrenheit and must be converted to Celsius. If the average spring temperature for New York was \(\displaystyle 50^{\circ}\) Fahrenheit, what is the temperature value in Celsius? 

The Fahrenheit to Celsius conversion equation is as follows:

\(\displaystyle T_{Celsius}=(T_{Fahrenheit}-32)\cdot \frac{5}{9}\)

Possible Answers:

\(\displaystyle 15^{\circ}\:C\)

\(\displaystyle 8^{\circ}\:C\)

\(\displaystyle 10^{\circ}\:C\) 

\(\displaystyle 6^{\circ}\:C\)

\(\displaystyle 12^{\circ}\:C\)

Correct answer:

\(\displaystyle 10^{\circ}\:C\) 

Explanation:

You can solve this problem by substituting in \(\displaystyle 50^{\circ}\) for \(\displaystyle T_{Fahrenheit}\) and solving for \(\displaystyle T_{Celsius}\):

\(\displaystyle T_{Celsius}=(50-32)\cdot \frac{5}{9}\)

\(\displaystyle T_{Celsius}=18\cdot \frac{5}{9}\)

\(\displaystyle T_{Celsius}=\frac{18}{1}\cdot\frac{5}{9}=\frac{18\cdot5}{1\cdot9}=\frac{90}{9}=10\)

That means that \(\displaystyle 50^{\circ}\) Fahrenheit is the same as \(\displaystyle 10^{\circ}\) Celsius.

Example Question #9 : Factoring

Factor to the simplest form:  \(\displaystyle x^3+2x^2+a+bx^2+2\)

Possible Answers:

\(\displaystyle 3x^3+a+b+2\)

\(\displaystyle x(x^2+2x+bx)+a+2\)

\(\displaystyle x^3+(2+b)(x^2)+a+2\)

\(\displaystyle x^2(x+2+b)+a+2\) 

\(\displaystyle x^2(x+2+b+a+2)\)

Correct answer:

\(\displaystyle x^2(x+2+b)+a+2\) 

Explanation:

Group all the terms with the \(\displaystyle x\) variable.

\(\displaystyle x^3+2x^2+a+bx^2+2= (x^3+2x^2+bx^2)+a+2\)

Pull out an \(\displaystyle x^2\) term from parentheses.

\(\displaystyle (x^3+2x^2+bx^2)+a+2 = x^2(x+2+b)+a+2\)

There are no more common factors.

The correct answer is:  \(\displaystyle x^2(x+2+b)+a+2\)

Example Question #10 : Factoring

A semi truck unloaded weighs \(\displaystyle 20,000\:lbs\). When the trailer compartment is loaded to half capacity with soda, the semi weighs \(\displaystyle 37,000\:lbs\). What will the truck weigh when the compartment is loaded to \(\displaystyle \frac{3}{4}\) capacity with the same kind of soda?

Possible Answers:

\(\displaystyle 25,500\:lbs\)

\(\displaystyle 56,000\:lbs\)

\(\displaystyle 45,500\:lbs\)

\(\displaystyle 54,000\:lbs\)

Correct answer:

\(\displaystyle 45,500\:lbs\)

Explanation:

This word problem can be broken down into a basic algebraic equation:

A half-loaded semi weighs 37,000 lbs. Subtracting the weight of the truck, we can determine that a half load weighs 17,000 lbs:

\(\displaystyle \frac{1}{2}x=37,000\:lbs-20,000\:lbs=17,000\:lbs\)

From that, we can determine that a full load = 34,000 lbs: 

\(\displaystyle 2\cdot \frac{1}{2}x=17,000\:lbs\cdot2=34,000\:lbs\)

Knowing the weight of a full load, we can calculate the weight of a 3/4 load:

\(\displaystyle \frac{3}{4}\cdot x=\frac{3}{4}\cdot34,000\:lbs=25,500\:lbs\)

Add the weight of the truck to get the total weight:

\(\displaystyle Weight=20,000\:lbs\cdot25,500\:lbs=45,500\:lbs\)

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