### All PSAT Math Resources

## Example Questions

### Example Question #111 : Psat Mathematics

A line graphed on the coordinate plane below.

Give the equation of the line in slope intercept form.

**Possible Answers:**

**Correct answer:**

The slope of the line is and the *y*-intercept is .

The equation of the line is .

### Example Question #2 : Graphing

Give the equation of the curve.

**Possible Answers:**

None of the other answers

**Correct answer:**

This is the parent graph of . Since the graph in question is negative, then we flip the quadrants in which it will approach infinity. So the graph of will start in quadrant 2 and end in 4.

### Example Question #112 : Psat Mathematics

The equation represents a line. This line does NOT pass through which of the four quadrants?

**Possible Answers:**

Cannot be determined

II

I

III

IV

**Correct answer:**

III

Plug in for to find a point on the line:

Thus, is a point on the line.

Plug in for to find a second point on the line:

is another point on the line.

Now we know that the line passes through the points and .

A quick sketch of the two points reveals that the line passes through all but the third quadrant.

### Example Question #3 : Graphing

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

**Possible Answers:**

**Correct answer:**

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 #4 : Graphing

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

**Possible Answers:**

**Correct answer:**

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 #5 : Graphing

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

**Possible Answers:**

**Correct answer:**

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

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