ACT Math : Algebra

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #2791 : Sat Mathematics

Let F(x) = x3 + 2x2 – 3 and G(x) = x + 5.  Find F(G(x))

Possible Answers:

x3x2x + 8

x3 + x2 + 2

x3 + 2x2 + x + 2

x3 + 17x2 + 95x + 172

x3 + 2x2 – x – 8

Correct answer:

x3 + 17x2 + 95x + 172

Explanation:

F(G(x)) is a composite function where the expression G(x) is substituted in for x in F(x)

F(G(x)) = (x + 5)3 + 2(x + 5)2 – 3 = x3 + 17x2 + 95x + 172

G(F(x)) = x3 + x2 + 2

F(x) – G(x) = x3 + 2x2 – x – 8

F(x) + G(x) =  x3 + 2x2 + x + 2

Example Question #2792 : Sat Mathematics

What is the value of xy2(xy – 3xy) given that = –3 and = 7?

Possible Answers:

–2881

3565

–6174

2881

Correct answer:

–6174

Explanation:

Evaluating yields –6174.

–147(–21 + 63) =

–147 * 42 = –6174

Example Question #2792 : Sat Mathematics

f(x)=x^{2}+2\displaystyle f(x)=x^{2}+2

g(x)=x-4\displaystyle g(x)=x-4

Find g(f(2))\displaystyle g(f(2)).

Possible Answers:

\dpi{100} \small 4

\dpi{100} \small 3

\dpi{100} \small 6

\dpi{100} \small 2

\dpi{100} \small 1

Correct answer:

\dpi{100} \small 2

Explanation:

g(f(2))\displaystyle g(f(2)) is \dpi{100} \small 2. To start, we find that f(2)=2^{2}+2=4+2=6\displaystyle f(2)=2^{2}+2=4+2=6. Using this, we find that g(6)=6-4=2\displaystyle g(6)=6-4=2.

Alternatively, we can find that g(f(x))=(x^{2}+2)-4=x^{2}-2\displaystyle g(f(x))=(x^{2}+2)-4=x^{2}-2. Then, we find that g(f(2))=2^{2}-2=4-2=2\displaystyle g(f(2))=2^{2}-2=4-2=2.

Example Question #2793 : Sat Mathematics

It takes no more than 40 minutes to run a race, but at least 30 minutes. What equation will model this in m minutes?

Possible Answers:

\left | m-35 \right |= 5\displaystyle \left | m-35 \right |= 5

\left | m-35 \right |< 5\displaystyle \left | m-35 \right |< 5

\left | m+35 \right |> 5\displaystyle \left | m+35 \right |> 5

\left | m+35 \right |< 5\displaystyle \left | m+35 \right |< 5

\left | m-35 \right |> 5\displaystyle \left | m-35 \right |> 5

Correct answer:

\left | m-35 \right |< 5\displaystyle \left | m-35 \right |< 5

Explanation:

If we take the mean number of minutes to be 35, then we need an equation which is less than 5 from either side of 35. If we subtract 35 from m\displaystyle m minutes and take the absolute value, this will give us our equation since we know that the time it takes to run the marathon is between 30 and 40 minutes.

Example Question #91 : Algebraic Functions

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

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

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

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

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

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 #2791 : Sat Mathematics

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

Possible Answers:

\displaystyle 1.5x - 2

\displaystyle 2x + 5

\displaystyle x + 4

\displaystyle 3x - 1

\displaystyle 2.5x - 8

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 #2796 : 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 \frac{1}{2}

\displaystyle \frac{7}{2}

\displaystyle 2

\displaystyle 0

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 #421 : Gre Quantitative Reasoning

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

Possible Answers:

x = 1

All real numbers are solutions.

x = 0

There are no solutions.

Correct answer:

There are no solutions.

Explanation:

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

Example Question #92 : Algebraic Functions

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 14

\displaystyle 19

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 #101 : 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}+2xh+h^{2}+3\displaystyle x^{2}+2xh+h^{2}+3

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

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

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

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

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.

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