PSAT Math : Algebra

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #986 : Psat Mathematics

If f(t)=6+(4-t)^2, what is the smallest possible value of f(t)?

Possible Answers:

4

6

8

12

10

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 #61 : Algebraic Functions

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

Possible Answers:

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

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

x^{2}+h^{2}

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

x^{2}+3+h

Correct answer:

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

Explanation:

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

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

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

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

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

Example Question #62 : Algebraic Functions

Letf(x)  and g(x) be functions such that f(x)=\frac{1}{x-3}, and f(g(x))=g(f(x))=x. Which of the following is equal to g(x)?

Possible Answers:

\frac{x}{x-3}

\frac{3x+1}{x}

\frac{x}{x+3}

\frac{1}{x+3}

\frac{4}{x}

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} y and \dpi{100} x, and then solving for \dpi{100} y.

We want to find the inverse of f(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} x and \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} x will be in the inverse of \dpi{100} f(x), which equals \dpi{100} g(x).

We can treat x = \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 #987 : Psat Mathematics

 .

Possible Answers:

Correct answer:

Explanation:

Example Question #989 : Psat Mathematics

Let the function f be defined by f(x)=x-t. If f(12)=4, what is the value of f(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 #63 : Algebraic Functions

Which of the following is equal to  if ?

Possible Answers:

Correct answer:

Explanation:

To solve, we can set the given function equal to six and solve for .

Add 3 to each side:

Take the square root. Remember that the root can be positive OR negative:

Subtract 3 from each side. It will be easiest to separate the equation into two parts:

Now we know that  is equal to  or . Based on the available answer options, the correct choice must be .

 

You can also solve this question by checking each answer option separately; you should find the same final answer.

Substitute each of the answer choices to see which one makes the equation equal to 6.

 

The answer to this question is . No other answer makes the equation equal 6.

 

Example Question #331 : Algebra

If  is an odd integer, and  is an even integer, which of the following must be even?

Possible Answers:

Correct answer:

Explanation:

Solve this problem using picked numbers. Choose an odd number to represent  and an even number to represent . In this case, we have chosen 3 to represent  and 2 to represent .

Substitute into each equation to find the correct answer:

This number is even, and likely the answer we are looking for. Just in case, quickly check the other answers to make sure no others come out even.

This expression gives an odd answer and must be incorrect.

This expression gives an odd answer and must be incorrect.

This expression gives an odd answer and must be incorrect.

This expression gives an odd answer and must be incorrect.

 

Only the first answer is even. The answer is .

Example Question #72 : How To Find F(X)

If  

What is ?

Possible Answers:

Correct answer:

Explanation:

To find f(4), input a 4 in every place you see an x in the equation. That gives you

When you simplify this expression, you get 

When you add together each part, you get

Example Question #332 : Algebra

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

Possible Answers:

0

–108

–12

96

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 #35 : Algebraic Functions

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

Possible Answers:

192

16

12

28

144

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.

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