PP-DS132

[max999]

If l and k are lines in the xy-plane, is the product of the slopes of l and k equal to -1 ?

(1) Line l passes through the origin and the point (1, 2).
(2) Line k has x-intercept 4 and y-intercept 2.

answer: C

[sunnyblue13s]

設y=ax+b
(1)把點代入公式求出斜率a1...unsufficient
(2)把點代入公式求出斜率a2...unsufficient

(1)+(2): a1*a2=-1....sufficient~!!.....(c)