PSAT Math : Coordinate Geometry

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #1 : Graphing


Psat1question

What is the equation of the line in the graph above?

Possible Answers:

Correct answer:

Explanation:

In order to find the equation of a line in slope-intercept form , where  is the slope and  is the y-intercept), one must know or otherwise figure out the slope of the line (its rate of change) and the point at which it intersects the y-axis. By looking at the graph, you can see that the line crosses the y-axis at .  Therefore, .

Slope is the rate of change of a line, which can be calculated by figuring out the change in y divided by the change in x, using the formula 

.  

When looking at a graph, you can pick two points on a graph and substitute their x-  and y-values into that equation.  On this graph, it's easier to choose points like and .  Plug them into the equation, and you get 

Plugging in those values for  and  in the equation, and you get 

Example Question #2 : Graphing

What are the x- and y- intercepts of the equation ?

Possible Answers:

Correct answer:

Explanation:

Answer: (1/2,0) and (0,-2)

Finding the y-intercept: The y-intercept is the point at which the line crosses tye y-axis, meaning that x = 0 and the format of the ordered pair is (0,y) with y being the y-intercept.  The equation  is in slope-intercept () form, meaning that the y-intercept, b, is actually given in the equation.  b = -2, which means that our y-intercept is -2.  The ordered pair for expressing this is (0,-2)

Finding the x-intercept: To find the x-intercept of the equation , we must find the point where the line of the equation crosses the x-axis.  In other words, we must find the point on the line where y is equal to 0, as it is when crossing the x-axis.  Therefore, substitute 0 into the equation and solve for x: 

The x-interecept is therefore (1/2,0).  

Example Question #3 : Graphing

Which of the following could be the equation of the line shown in this graph?

Line

Possible Answers:

Correct answer:

Explanation:

The line in the diagram has a negative slope and a positive y-intercept. It has a negative slope because the line moves from the upper left to the lower right, and it has a positive y-intercept because the line intercepts the y-axis above zero. 

The only answer choice with a negative slope and a positive y-intercept is 

Example Question #1 : How To Graph An Ordered Pair

Which of the following coordinate pairs is farthest from the origin?

Possible Answers:

Correct answer:

Explanation:

Using the distance formula, calculate the distance from each of these points to the origin, (0, 0). While each answer choice has coordinates that add up to seven, (-1, 8) is the coordinate pair that produces the largest distance, namely , or approximately 8.06.

Example Question #4 : Graphing

A point at  in the standard coordinate plane is shifted right 5 units and down 3 units.  What are the new coordinates of the point?

Possible Answers:

Correct answer:

Explanation:

The point  shifted to the right 5 units will shift along the x-axis, meaning that you will add 5 to the original x-coordinate, so the new . The point shifted down by three units will shift down the y-axis, meaning that you will subtract three from the original y-coordinate, so the new .

The resultant coordinate is .  

Example Question #121 : Coordinate Geometry

Axes_1

Give the coordinates of the point plotted in the above set of coordinate axes.

Possible Answers:

None of the other responses is correct.

Correct answer:

Explanation:

The point can be reached from the origin by moving 2 units right then 6 units up. This makes the first coordinate 2 and the second coordinate 6.

Example Question #1 : How To Graph A Function

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

Possible Answers:

3

7

4

5

6

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 #2 : How To Graph A Function

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

6

3

4

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 #11 : How To Graph A Function

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 #4 : 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:

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