McGraw-Hill Education GRE 2019

Parallel and Perpendicular Lines

If two lines are parallel, then their slopes are equal and the lines never intersect.

(See figure.)

y

x

If two lines are perpendicular, then the product of their slopes is −1. Another way

to say this is that their slopes are negative reciprocals. (See figure.)

m = –2

–2 ×= –1

m =^12

1

2

y

x

Line k is defined by the equation y = 2x – 3. Lines l and m are each

perpendicular to line k.

QUANTITY A QUANTITY B

the slope of line k the sum of the slopes

of lines l and m

SOLUTION: Since the equation for line k is y = 2x – 3, you know that the slope

of line k is 2. Since lines l and m are perpendicular to line k, each of their

slopes is the negative reciprocal of 2: −^12. −^12 + −^12 = −1. Quantity A is greater.

436 PART 4 ■ MATH REVIEW

04-GRE-Test-2018_313-462.indd 436 12/05/17 12:06 pm