ACT Math : ACT Math

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #263 : Coordinate Geometry

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 x2 terms 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 #261 : Coordinate Geometry

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

Possible Answers:

6

4

7

3

5

Correct answer:

3

Explanation:

The graph is a down-opening parabola with a maximum of y=3. Therefore, there are no y values greater than this for this function.

Example Question #5 : How To Graph A Function

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

 where  is the  intercept and  is the slope.

The  intercept can be found by noting the point where the line and the y-axis cross, in this case, at  so .

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 #264 : Coordinate Geometry

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

Possible Answers:

Function_graph_2

Function_graph_3

Function_graph_4

Function_graph_1

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 of  when .

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

So the y-intercept is at .

Example Question #265 : Coordinate Geometry

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

Possible Answers:

Function_graph_5

Function_graph_8

Function_graph_6

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 of  for which .

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

So the x-intercept is at .

Example Question #266 : Coordinate Geometry

Which of the following represents ?

Possible Answers:

Function_graph_12

Function_graph_11

Function_graph_10

Function_graph_9

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 #1 : Graphing

Suppose

To obtain the graph of , shift the graph  a distance of  units              .

Possible Answers:

Up and right

To the left

Upwards

To the right

Downwards

Correct answer:

Upwards

Explanation:

There are four shifts of the graph y = f(x):

y = f(x) + c shifts the graph c units upwards.

y = f(x) – c shifts the graph c units downwards.

y = f(x + c) shifts the graph c units to the left.

y = f(x – c) shifts the graph c units to the right.

Example Question #841 : Act Math

Which of the following graphs does NOT represent a function?

Possible Answers:

All of the graphs are functions.

Act_math_159_13

Act_math_159_10

Act_math_159_14

Act_math_159_12

Correct answer:

Act_math_159_13

Explanation:

This question relies on both the vertical-line test and the definition of a function. We need to use the vertical-line test to determine which of the graphs is not a function (i.e. the graph that has more than one output for a given input). The vertical-line test states that a graph represents a function when a vertical line can be drawn at every point in the graph and only intersect it at one point; thus, if a vertical line is drawn in a graph and it intersects that graph at more than one point, then the graph is not a function. The circle is the only answer choice that fails the vertical-line test, and so it is not a function.

Example Question #842 : Act Math

How would you plot the point ?

Possible Answers:

From the origin, go right  units, and up  units

From the origin, go up  units, and right  units

From the origin, go right  units, and down  units

From the origin, go left  units, and up  units

Correct answer:

From the origin, go right  units, and up  units

Explanation:

For the ordered pair 

The first number is for the x-axis, so because it is positive you go right .

The second number is for the y-axis, so because it is positive you go up .

Example Question #843 : Act Math

How would you plot the point ?

Possible Answers:

From the origin, go right  units, and down  units

 

From the origin, go right  units, and up  units

 

From the origin, go left  units, and up  units

 

From the origin, go left  units, and down  units

 

Correct answer:

From the origin, go left  units, and up  units

 

Explanation:

For the ordered pair  we would do the following.

The first number is for the x-axis, so because it is negative you go left  units.

The second number is for the y-axis, so because it is positive you go up  units.

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