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DS-5
Source: Beat The GMAT — Data Sufficiency |
Yes, C is the right answer.
I was thinking about it and got this explanation.
Let,
L = y1 = m1x1+C1, y-i'cept = c1, x-i'cept = -c1/m1
M = y2=m2x2+C2, y-i'cept = c2, x-i'cept = -c2/m2
Q: is m1m2 <0>0, insuff since c1c2 and m1m2 could be -ve or +ve at the same time and satisfy.
choice 2). c1c2< 0 , insuff since no info about m1m2
combined): m1m2 must be <0
I was thinking about it and got this explanation.
Let,
L = y1 = m1x1+C1, y-i'cept = c1, x-i'cept = -c1/m1
M = y2=m2x2+C2, y-i'cept = c2, x-i'cept = -c2/m2
Q: is m1m2 <0>0, insuff since c1c2 and m1m2 could be -ve or +ve at the same time and satisfy.
choice 2). c1c2< 0 , insuff since no info about m1m2
combined): m1m2 must be <0
