SAT Math : How to find f(x)

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #131 : How To Find F(X)

Define the function  as follows:

Give the range of .

Possible Answers:

Correct answer:

Explanation:

Since the piecewise-defined function  is defined two different ways, one for negative numbers and one for nonnegative numbers, examine both definitions and determine each partial range separately;  the union of the partial ranges will be the overall range.

If , then 

 

Since 

,

applying the properties of inequality,

Therefore, on the portion of the domain comprising nonpositive numbers, the partial range of  is the set .

 

If , then 

 

Since 

,

applying the properties of inequality,

Therefore, on the portion of the domain comprising positive numbers, the partial range of  is the set .

 

The overall range is the union of these partial ranges, which is .

Example Question #171 : Algebraic Functions

Define  , restricting the domain of the function to  .

Determine  (you need not determine its domain restriction).

Possible Answers:

 does not exist

Correct answer:

 does not exist

Explanation:

First, we must determine whether  exists.

A quadratic function has a parabola as its graph; this graph decreases, then increases (or vice versa), with a vertex at which the change takes place. 

 exists if and only if, if , then - or, equivalently, if there does not exist  and  such that , but . This will happen on any interval on which the graph of  constantly increases or constantly decreases, but if the graph changes direction on an interval, there will be  such that  on this interval. The key is therefore to determine whether the interval to which the domain is restricted contains the vertex.

The -coordinate of the vertex of the parabola of the function

is .

The -coordinate of the vertex of the parabola of  can be found by setting :

.

The vertex of the graph of  without its domain restriction is at the point with -coordinate 4. Since , the vertex is in the interior of the domain; as a consequence,  does not exist on .

Example Question #1103 : Algebra

Define , restricting the domain to .

Give the range of .

Possible Answers:

 

Correct answer:

 

Explanation:

A function of the form  is a linear function and is either constantly increasing or constantly decreasing. Therefore, we can simply note that if

,

as stated in the domain, then, multiplying both sides by , remembering to switch the symbol since we are multiplying by a negative number:

Add 12 to both sides:

Replacing, we see that 

,

so the range of  is .

Example Question #172 : Algebraic Functions

Define , restricting the domain of the function to the interval .

Give the range of the function.

Possible Answers:

Correct answer:

Explanation:

If , it follows by applying the properties of inequality that:

Multiply both sides by , which must be positive by closure:

that is, 

Also,by closure, , so

This makes the correct range .

Example Question #2881 : Sat Mathematics

Find  in terms of .

Possible Answers:

Correct answer:

Explanation:

Substitute 6x for x in the f(x) function and simplify.

Example Question #2881 : Sat Mathematics

If a function has x-intercepts at , and at , what is the equation?

Possible Answers:

Correct answer:

Explanation:

Since we are given the functions x-intercepts, we can write the equation as , now we need to use FOIL.

Start with .

Now we do

 

Example Question #2882 : Sat Mathematics

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Approximate the Average Yearly change in the number of PhD's.

Possible Answers:

Correct answer:

Explanation:

What this question is asking for is to approximate the slope of the line of best fit. To calculate the slope, we need to find find two points on the line. The best points to pick out is , and . Now we can find the rate of change by using the following equation.

, where  are points on the line.

 

Example Question #138 : How To Find F(X)

Set up the equation:  The sum of two times a number and forty is equal to sixteen.

Possible Answers:

Correct answer:

Explanation:

Break up the problem into parts.

Two times a number:  

 The sum of two times a number and forty:  

Is equal to sixteen:  

Combine the terms to form the equation.

The answer is:  

Example Question #139 : How To Find F(X)

Set up the following equation:  Three less than the square of a number is eleven.

Possible Answers:

Correct answer:

Explanation:

Split up the question into parts.

The square of a number:  

Three less than the square of a number:  

Is eleven:  

Combine the terms.

The answer is:  

Example Question #131 : How To Find F(X)

Set up the equation:

The difference of six and a number squared is four.

Possible Answers:

Correct answer:

Explanation:

Write the following sentence by parts.

A number squared:  

The difference of six and a number squared:  

Is four:  

Combine the parts to write an equation.

The answer is:  

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