All PSAT Math Resources
Example Questions
Example Question #1 : Graphing
What is the equation of the line in the graph above?
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 ?
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?
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?
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?
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
Give the coordinates of the point plotted in the above set of coordinate axes.
None of the other responses is correct.
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 for ?
The graph is a down-opening parabola with a maximum of . Therefore, there are no y values greater than this for this function.
Example Question #2 : How To Graph A Function
The figure above shows the graph of y = f(x). Which of the following is the graph of y = |f(x)|?
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 ?
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
What is the equation for the line pictured above?
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: