# SSAT Upper Level Math : How to find whether lines are perpendicular

## Example Questions

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### Example Question #4 : Properties Of Parallel And Perpendicular Lines

Three lines are drawn on the coordinate plane.

The green line has slope , and -intercept .

The blue line has slope , and  -intercept .

The red line has slope , and -intercept .

Which two lines are perpendicular to each other?

The blue line and the green line are perpendicular.

The green line and the red line are perpendicular.

It cannot be determined from the information given.

No two of these lines are perpendicular.

The blue line and the red line are perpendicular.

The blue line and the red line are perpendicular.

Explanation:

To demonstrate two perpendicular lines, multiply their slopes; if their product is , then the lines are perpendicular (the -intercepts are irrelevant).

The products of these lines are given here.

Blue and green lines:

Red and green lines:

Blue and red lines:

It is the blue and red lines that are perpendicular.

We can also see that their slopes are negative reciprocals, indicating perpendicular lines.

### Example Question #5 : Properties Of Parallel And Perpendicular Lines

Two perpendicular lines intersect at point . One line also includes point . What is the slope of the other line?

Insufficient information is given to answer the question.

Explanation:

The slopes of two perpendicular lines are the opposites of each other's reciprocals.

To find the slope of the first line substitute  in the slope formula:

The slope of the first line is , so the slope of the second line is the opposite reciprocal of this, which is .

### Example Question #6 : Properties Of Parallel And Perpendicular Lines

Two perpendicular lines intersect at the origin; one line also passes through point . What is the slope of the other line?

Insufficient information is given to solve the problem.

Explanation:

The slopes of two perpendicular lines are the opposites of each other's reciprocals.

To find the slope of the first line, substitute  in the slope formula:

The slope of the first line is , so the slope of the second line is the opposite reciprocal of this, which is .

### Example Question #11 : Properties Of Parallel And Perpendicular Lines

Which of the following lines is perpendicular to the line ?

Explanation:

All we care about for this problem is the slopes of the lines...the x- and y-intercepts are irrelevant.

Remember that the slopes of perpendicular lines are opposite reciprocals. By putting the given equation into  form, we can see that its slope is . So we are looking for a line with a slope of .

The equation  can be put into the form , and so we know that it is perpendicular to the given line.

### Example Question #12 : Properties Of Parallel And Perpendicular Lines

Line A passes through the origin and .

Line B passes through the origin and .

Line C passes through the origin and .

Line D passes through the origin and .

Line E passes through the origin and .

Which line is perpendicular to Line A?

Line D

None of the other lines is perpendicular to A.

Line B

Line C

Line E

Line D

Explanation:

Find the slopes of all five lines using the slope formula . Since each line passes through the origin, this formula can be simplified to

using the other point.

Line A:

The correct line must have as its slope the opposite of the reciprocal of this, which is .

Line B:

Line C:

Line D:

Line E:

Of the last four lines, only Line D has the desired slope.

### Example Question #13 : Properties Of Parallel And Perpendicular Lines

Line W passes through the origin and point .

Line X passes through the origin and point .

Line Y passes through the origin and point .

Line Z passes through the origin and point .

Which of these lines is perpendicular to the line of the equation  ?

Line X

Line Z

None of the other responses is correct.

Line W

Line Y

Line Z

Explanation:

First, find the slope of the line of the equation  by rewriting it in slope-intercept form:

The slope of this line is , so we are looking for a line whose slope is the opposite of the reciprocal of this, or

Find the slopes of all four lines by using the slope formula . Since each line passes through the origin, this formula can be simplified to

using the other point.

Line W:

Line X:

Line Y:

Line Z:

Line Z has the desired slope and is the correct choice.

### Example Question #14 : Properties Of Parallel And Perpendicular Lines

Determine whether the two equations are parallel, perpendicular or neither, and choose the best reason.

Neither, the slopes have no correlation.

Perpendicular, the slopes are the negative reciprocal to each other.

Parallel, the slopes are the same.

Perpendicular, the slopes are the same.

Parallel, the slopes are the negative reciprocal to each other.

Neither, the slopes have no correlation.

Explanation:

Convert both equations to slope intercept form:

The slope of the first equation is .

Convert the second equation.

The slope of this equation is zero since there is no  term!

In order for the two functions to be parallel, they must have the same slopes.

In order for the two functions to be perpendicular, their slopes must be the negative reciprocal to each other.

Since there's no correlation with both slopes, the equations are neither parallel or perpendicular to each other.

Neither, the slopes have no correlation

### Example Question #15 : Properties Of Parallel And Perpendicular Lines

Given: the following three lines on the coordinate plane:

Line 1: The line of the equation

Line 2: The line of the equation

Line 3: The line of the equation

Which of the following is a true statement?

Line 1 and Line 3 are perpendicular; Line 2 is perpendicular to neither.

No two of Line 1, Line 2, or Line 3 form a pair of perpendicular lines.

Line 1 and Line 2 are perpendicular; Line 3 is perpendicular to neither.

None of the other responses is correct.

Line 2 and Line 3 are perpendicular; Line 1 is perpendicular to neither.

Line 1 and Line 2 are perpendicular; Line 3 is perpendicular to neither.

Explanation:

Line 1, the line of the equation , is a vertical line on the coordinate plane; Line 2, the line of the equation , is a horizontal line. Lines 1 and 2 are perpendicular to each other.

The slope of Line 3, the line of the equation , can be calculated by putting the equation in slope-intercept form:

The slope is , which makes it perpendicular to a line of slope . Line 1, being vertical, has undefined slope, and Line 2, being horizontal, has slope 0.

Correct response: Line 1 and Line 2 are perpendicular; Line 3 is perpendicular to neither.

### Example Question #16 : Properties Of Parallel And Perpendicular Lines

The line of the equation  is perpendicular to which of the following lines on the coordinate plane?

None of the other responses is correct.

Explanation:

First, find the slope of the line  by rewriting the equation in slope-intercept form and noting the coefficient of :

The line has slope .

A line perpendicular to this would have slope . Of the four equations among the choices, all of which are in slope-intercept form, only  has this slope.

### Example Question #17 : Properties Of Parallel And Perpendicular Lines

One side of a rectangle on the coordinate plane has as its endpoints the points  and .

What would be the slope of a side adjacent to this side?

None of the other responses gives the correct answer.

Explanation:

First, we find the slope of the segment connecting  or . Using the formula

and setting

we get

Adjacent sides of a rectangle are perpendicuar, so their slopes will be the opposites of each other's reciprocals. Therefore, the slope of an adjacent side will be the opposite of the reciprocal of , which is .

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