SAT Math : How to graph a function

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #2 :Graphing

Which of the following could be a value off(x)forf(x)=-x^2 + 3?

Possible Answers:

7

3

4

6

5

Correct answer:

3

Explanation:

图为down-opening抛物线极限m ofy=3. Therefore, there are no y values greater than this for this function.

Example Question #3 :Graphing

2

The figure above shows the graph of y = f(x). Which of the following is the graph of y = |f(x)|?

Possible Answers:

5

2

4

3

6

Correct answer:

2

Explanation:

One of the properties of taking an absolute value of a function is that the values are all made positive. The values themselves do not change; only their signs do. In this graph, none of the y-values are negative, so none of them would change. Thus the two graphs should be identical.

Example Question #4 :Graphing

Below is the graph of the function:

Which of the following could be the equation for?

Possible Answers:

Correct answer:

Explanation:

First, because the graph consists of pieces that are straight lines, the function must include an absolute value, whose functions usually have a distinctive "V" shape. Thus, we can eliminate f(x) = x2– 4x + 3 from our choices. Furthermore, functions with x2terms are curved parabolas, and do not have straight line segments. This means that f(x) = |x2– 4x| – 3 is not the correct choice.

Next, let's examine f(x) = |2x – 6|. Because this function consists of an abolute value by itself, its graph will not have any negative values. An absolute value by itself will only yield non-negative numbers. Therefore, because the graph dips below the x-axis (which means f(x) has negative values), f(x) = |2x – 6| cannot be the correct answer.

Next, we can analyze f(x) = |x – 1| – 2. Let's allow x to equal 1 and see what value we would obtain from f(1).

f(1) = | 1 – 1 | – 2 = 0 – 2 = –2

However, the graph above shows that f(1) = –4. As a result, f(x) = |x – 1| – 2 cannot be the correct equation for the function.

By process of elimination, the answer must be f(x) = |2x – 2| – 4. We can verify this by plugging in several values of x into this equation. For example f(1) = |2 – 2| – 4 = –4, which corresponds to the point (1, –4) on the graph above. Likewise, if we plug 3 or –1 into the equation f(x) = |2x – 2| – 4, we obtain zero, meaning that the graph should cross the x-axis at 3 and –1. According to the graph above, this is exactly what happens.

The answer is f(x) = |2x – 2| – 4.

Example Question #201 :Coordinate Plane

Screen_shot_2015-03-06_at_2.14.03_pm

What is the equation for the line pictured above?

Possible Answers:

Correct answer:

Explanation:

A line has the equation

whereis theintercept andis the slope.

Theintercept can be found by noting the point where the line and the y-axis cross, in this case, atso.

The slope can be found by selecting two points, for example, the y-intercept and the next point over that crosses an even point, for example,.

Now applying the slope formula,

which yields.

Therefore the equation of the line becomes:

Example Question #6 :Graphing

Which of the following graphs represents the y-intercept of this function?

Possible Answers:

Function_graph_4

Function_graph_1

Function_graph_3

Function_graph_2

Correct answer:

Function_graph_1

Explanation:

Graphically, the y-intercept is the point at which the graph touches the y-axis. Algebraically, it is the value ofwhen.

Here, we are given the function. In order to calculate the y-intercept, setequal to zero and solve for.

So the y-intercept is at.

Example Question #7 :Graphing

Which of the following graphs represents the x-intercept of this function?

Possible Answers:

Function_graph_5

Function_graph_6

Function_graph_8

Function_graph_7

Correct answer:

Function_graph_6

Explanation:

Graphically, the x-intercept is the point at which the graph touches the x-axis. Algebraically, it is the value offor which.

Here, we are given the function. In order to calculate the x-intercept, setequal to zero and solve for.

So the x-intercept is at.

Example Question #8 :Graphing

Which of the following represents?

Possible Answers:

Function_graph_12

Function_graph_9

Function_graph_11

Function_graph_10

Correct answer:

Function_graph_9

Explanation:

A line is defined by any two points on the line. It is frequently simplest to calculate two points by substituting zero for x and solving for y, and by substituting zero for y and solving for x.

Let. Then

So our first set of points (which is also the y-intercept) is

Let. Then

So our second set of points (which is also the x-intercept) is.

Example Question #9 :Graphing

The graphic shows Bob's walk. At what times is Bob the furthest from home?

Screen shot 2016 02 18 at 8.42.52 am

Possible Answers:

to

to

Correct answer:

to

Explanation:

If we look at the graph, the line segment fromto, is the furthest from home. So the answer will be fromto.

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