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