1.

Lines x = ay + b, z = cy + dand x = a'y + b', z = c'y + d'are perpendicular, if

A. aa' + cc' + 1 = 0
B. aa' + cc' - 1 = 0
C. ac + a'c' -1 = 0
D. ac + a'c' + 1 = 0
Answer» B. aa' + cc' - 1 = 0


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