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Vector Algebra

Question
CBSEENMA12036302

The length of the projection of the line segment joining the points (5, –1, 4) and (4, –1, 3) on the plane, x + y + z = 7 is:

  • 23

  • 23

  • 2/3

  • 1/3

Solution

A.

23

Normal to the plane x + y +z = 7 is

n = i^ + j^ + k^AB = - i^ - k^  AB = AB = 2BC = Length of projection of AB on n = |AB.n|= (-i^ - k^). ( i^ + j^ + k^)3 = 23Length of projection of the line segment on the plane is ACAC2 = AB2 - BC2 = 2-43 = 23AC2 = 23