SAT Math : How to find f(x)

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #102 :Algebraic Functions

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Correct answer:

Explanation:

When we multiply a function by a constant, we multiply each value in the function by that constant. Thus, 2f(x) = 4x + 12. We then subtract g(x) from that function, making sure to distribute the negative sign throughout the function. Subtracting g(x) from 4x + 12 gives us 4x + 12 - (3x - 3) = 4x + 12 - 3x + 3 = x + 15. We then add 2 to x + 15, giving us our answer ofx + 17.

Example Question #103 :Algebraic Functions

Given the following functions, evaluate.

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Correct answer:

Explanation:

Example Question #104 :Algebraic Functions

The pointis one of the points of intersection of the graphs ofand. Given thatand, find the value of.

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Correct answer:

Explanation:

Since it’s given than, we know that. We now know that (3, 7) is a point of intersection. Therefore,as well. In other words,, so.

Example Question #105 :Algebraic Functions

Consider these functions:

Which of the following is equivalent to?

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Correct answer:

Explanation:

Example Question #106 :Algebraic Functions

Iff(t)=6+(4-t)^2, what is the smallest possible value off(t)?

Possible Answers:

4

12

10

6

8

Correct answer:

6

Explanation:

This equation describes a parabola whose vertex is located at the point (4, 6). No matter how large or small the value of t gets, the smallest that f(t) can ever be is 6 because the parabola is concave up. To prove this to yourself you can plug in different values of t and see if you ever get anything smaller than 6.

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Example Question #12 :Algebraic Functions

Iff(x)=x^{2}+3, thenf(x+h)=?

Possible Answers:

x^{2}+3+h

x^{2}+h^{2}

x^{2}+2xh+h^{2}+3

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

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

Correct answer:

x^{2}+2xh+h^{2}+3

Explanation:

To findf(x+h)whenf(x)=x^{2}+3, we substitute(x+h)forxinf(x).

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

We expand(x+h)^{2}tox^{2}+xh+xh+h^{2}.

We can combine like terms to getx^{2}+2xh+h^{2}.

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

Example Question #101 :Algebraic Functions

Letf(x)andg(x)be functions such thatf(x)=\frac{1}{x-3}, andf(g(x))=g(f(x))=x. Which of the following is equal tog(x)?

Possible Answers:

\frac{4}{x}

\frac{x}{x+3}

\frac{1}{x+3}

\frac{3x+1}{x}

\frac{x}{x-3}

Correct answer:

\frac{3x+1}{x}

Explanation:

If\dpi{100} h(x)and\dpi{100} k(x)are defined as inverse functions, then\dpi{100} h(k(x))=k(h(x))=x. Thus, according to the definition of inverse functions,\dpi{100} f(x)and\dpi{100} g(x)given in the problem must be inverse functions.

If we want to find the inverse of a function, the most straighforward method is usually replacing\dpi{100} f(x)with\dpi{100} y, swapping\dpi{100} yand\dpi{100} x, and then solving for\dpi{100} y.

We want to find the inverse off(x)=\frac{1}{x-3}. First, we will replace\dpi{100} f(x)with\dpi{100} y.

y = \frac{1}{x-3}

Next, we will swap\dpi{100} xand\dpi{100} y.

x = \frac{1}{y-3}

Lastly, we will solve for\dpi{100} y. The equation that we obtain in terms of\dpi{100} xwill be in the inverse of\dpi{100} f(x), which equals\dpi{100} g(x).

We can treatx = \frac{1}{y-3}as a proportion,\frac{x}{1} = \frac{1}{y-3}. This allows us to cross multiply and set the results equal to one another.

x(y-3)= 1

We want to get y by itself, so let's divide both sides by x.

y-3=\frac{1}{x}

Next, we will add 3 to both sides.

y=\frac{1}{x}+3

To combine the right side, we will need to rewrite 3 so that it has a denominator of\dpi{100} x.

y=\frac{1}{x}+3 = \frac{1}{x}+\frac{3x}{x}=\frac{3x+1}{x}

The answer is\frac{3x+1}{x}.

Example Question #108 :Algebraic Functions

.

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Correct answer:

Explanation:

Example Question #2811 :Sat Mathematics

Let the functionfbe defined byf(x)=x-t. Iff(12)=4, what is the value off(0.5*t)?

Possible Answers:

Correct answer:

Explanation:

First we substitute in 12 for x and set the equation up as 12-t=4. We then get t=8, and substitute that for t and get f(0.5*8), giving us f(4). Plugging 4 in for x, and using t=8 that we found before, gives us:

f(4) = 4 - 8 = -4

Example Question #71 :Algebraic Functions

What is the value of the function f(x) = 6x2+ 16x – 6 when x = –3?

Possible Answers:

96

–12

–108

0

Correct answer:

0

Explanation:

有两种方法可以解决这个问题。第一个way just involves plugging in –3 for x and solving 6〖(–3)〗2+ 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).

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