GRE Math : Algebra

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #2795 : Sat Mathematics

If \small f(x) = 4x^{2}+3x+2\(\displaystyle \small f(x) = 4x^{2}+3x+2\) and \small g(x) = x+7\(\displaystyle \small g(x) = x+7\), what is \small f(g(x))\(\displaystyle \small f(g(x))\)?

Possible Answers:

\small 4x^{2}+17x+219\(\displaystyle \small 4x^{2}+17x+219\)

\small 4x^{2}+3x+219\(\displaystyle \small 4x^{2}+3x+219\)

\small 4x^{2}+59x+219\(\displaystyle \small 4x^{2}+59x+219\)

\small 4x^{2}+17x+72\(\displaystyle \small 4x^{2}+17x+72\)

\small 4x^{2}+3x+72\(\displaystyle \small 4x^{2}+3x+72\)

Correct answer:

\small 4x^{2}+59x+219\(\displaystyle \small 4x^{2}+59x+219\)

Explanation:

\small 4(x+7)^{2} +3(x+7)+2\(\displaystyle \small 4(x+7)^{2} +3(x+7)+2\)

\small 4(x^{2} + 14x + 49)+ 3x +21 + 2\(\displaystyle \small 4(x^{2} + 14x + 49)+ 3x +21 + 2\)

\small 4x^{2}+56x+196+3x+23\(\displaystyle \small 4x^{2}+56x+196+3x+23\)

\small 4x^{2}+59x+219\(\displaystyle \small 4x^{2}+59x+219\)

Example Question #2796 : Sat Mathematics

If \(\displaystyle f(6)=7\) and \(\displaystyle f(10)=17\), which of the following could represent \(\displaystyle f(x)\)?

Possible Answers:

\(\displaystyle 2.5x - 8\)

\(\displaystyle 1.5x - 2\)

\(\displaystyle x + 4\)

\(\displaystyle 2x + 5\)

\(\displaystyle 3x - 1\)

Correct answer:

\(\displaystyle 2.5x - 8\)

Explanation:

The number in the parentheses is what goes into the function.

For the function \(\displaystyle f(x) = 2.5x - 8\),

\(\displaystyle f(6) = 2.5(6) - 8 = 7\) and

\(\displaystyle f(10) = 2.5(10) - 8 = 17\)

Example Question #2800 : Sat Mathematics

A function F is defined as follows:

for x2 > 1, F(x) = 4x2 + 2x – 2

for x2 < 1, F(x) = 4x2 – 2x + 2

What is the value of F(1/2)?

Possible Answers:

\(\displaystyle 4\)

\(\displaystyle 0\)

\(\displaystyle \frac{1}{2}\)

\(\displaystyle \frac{7}{2}\)

\(\displaystyle 2\)

Correct answer:

\(\displaystyle 2\)

Explanation:

For F(1/2), x2=1/4, which is less than 1, so we use the bottom equation to solve. This gives F(1/2)= 4(1/2)2 – 2(1/2) + 2 = 1 – 1 + 2 = 2

Example Question #2801 : Sat Mathematics

Which of the statements describes the solution set for 7(x + 3) = 7x + 20 ? 

Possible Answers:

x = 1

All real numbers are solutions.

There are no solutions.

x = 0

Correct answer:

There are no solutions.

Explanation:

By distribution we obtain 7x – 21 = – 7x + 20. This equation is never possibly true.

Example Question #11 : How To Find F(X)

Will just joined a poetry writing group in town that meets once a week. The number of poems Will has written after a certain number of meetings can be represented by the function \(\displaystyle f(p) = 2p+6\), where \(\displaystyle p\) represents the number of meetings Will has attended. Using this function, how many poems has Will written after 7 classes?

Possible Answers:

\(\displaystyle 20\)

\(\displaystyle 21\)

\(\displaystyle 15\)

\(\displaystyle 19\)

\(\displaystyle 14\)

Correct answer:

\(\displaystyle 20\)

Explanation:

For this function, simply plug 7 in for \(\displaystyle p\) and solve:

\(\displaystyle f(p)=2p+6=2(7)+6=20\)

Example Question #62 : Algebraic Functions

If f(x)=x^{2}+3\(\displaystyle f(x)=x^{2}+3\), then f(x+h)=\(\displaystyle f(x+h)=\) ?

Possible Answers:

x^{2}+3+h\(\displaystyle x^{2}+3+h\)

x^{2}+h^{2}+3\(\displaystyle x^{2}+h^{2}+3\)

x^{2}+2xh+h^{2}\(\displaystyle x^{2}+2xh+h^{2}\)

x^{2}+2xh+h^{2}+3\(\displaystyle x^{2}+2xh+h^{2}+3\)

x^{2}+h^{2}\(\displaystyle x^{2}+h^{2}\)

Correct answer:

x^{2}+2xh+h^{2}+3\(\displaystyle x^{2}+2xh+h^{2}+3\)

Explanation:

To find f(x+h)\(\displaystyle f(x+h)\) when f(x)=x^{2}+3\(\displaystyle f(x)=x^{2}+3\), we substitute (x+h)\(\displaystyle (x+h)\) for x\(\displaystyle x\) in f(x)\(\displaystyle f(x)\).

Thus, f(x+h)=(x+h)^{2}+3\(\displaystyle f(x+h)=(x+h)^{2}+3\).

We expand (x+h)^{2}\(\displaystyle (x+h)^{2}\)  to x^{2}+xh+xh+h^{2}\(\displaystyle x^{2}+xh+xh+h^{2}\).

We can combine like terms to get x^{2}+2xh+h^{2}\(\displaystyle x^{2}+2xh+h^{2}\).

We add 3 to this result to get our final answer.

Example Question #12 : How To Find F(X)

What is the value of the function f(x) = 6x+ 16x – 6 when x = –3?

Possible Answers:

–108

96

0

–12

Correct answer:

0

Explanation:

There are two ways to do this problem. The first way just involves plugging in –3 for x and solving 6〖(–3)〗+ 16(–3) – 6, which equals 54 – 48 – 6 = 0. The second way involves factoring the polynomial to (6x – 2)(x + 3) and then plugging in –3 for x. The second way quickly shows that the answer is 0 due to multiplying by (–3 + 3).

Example Question #13 : How To Find F(X)

Given the functions f(x) = 2x + 4 and g(x) = 3x – 6, what is f(g(x)) when = 6?

Possible Answers:

144

12

16

28

192

Correct answer:

28

Explanation:

We need to work from the inside to the outside, so g(6) = 3(6) – 6 = 12.

Then f(g(6)) = 2(12) + 4 = 28.

Example Question #1041 : Algebra

A function f(x) = –1 for all values of x. Another function g(x) = 3x for all values of x. What is g(f(x)) when x = 4?

Possible Answers:

–1

3

–12

–3

12

Correct answer:

–3

Explanation:

We work from the inside out, so we start with the function f(x). f(4) = –1. Then we plug that value into g(x), so g(f(x)) = 3 * (–1) = –3.

Example Question #1042 : Algebra

What is f(–3) if f(x) = x2 + 5?

Possible Answers:

4

14

15

–14

–4

Correct answer:

14

Explanation:

f(–3) = (–3)2 + 5 = 9 + 5 = 14

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