either one by itself is insufficient, b/c you can have the slope product be - while satisfying the condition.
make a table for each condition with 2 possible cases that satisfy the condition:
X:
L + -
K + -
Y:
L + -
K - +
when x and y signs are the same, we get a negative slope and a positive one when they are opposite. now match X with Y case by case and imagine what slopes these lines have to convince yourself.
both statements are sufficient together.
i don't think there's an easy way to this. you just have to be good at drawing lines in your head.
DS Quesiton
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Source: Beat The GMAT — Data Sufficiency |
