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a x - b y = k and c x - d y = k*

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sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 amFollowed by: 80 members; Location: India; Thanked: 267 times; GMAT Score:760

by sanju09 » Tue Jan 12, 2010 4:35 am

If the straight lines a x - b y = k and c x - d y = k* are perpendicular to each other, then what is the relation between a, b, c & d?
(A) a d + b c = 0
(B) a b + c d = 0
(C) a b - c d = 0
(D) a c - b d = 0
(E) a c + b d = 0

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Source: Beat The GMAT — Problem Solving | Tue Jan 12, 2010 4:35 am

truplayer256: Master | Next Rank: 500 Posts; Posts: 392; Joined: Thu Jan 15, 2009 12:52 pm; Location: New Jersey; Thanked: 76 times

by truplayer256 » Tue Jan 12, 2010 5:27 am

ax-by=k-->y=(ax-k)/b

m=slope=a/b

cx-dy=k*-->y=(cx-k*)/d

m=slope=c/d

c/d=-b/a

ac=-bd

ac+bd=0

E

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