Question

Please answer it urgent And I am goona mark it as brainellist.........

Answer 1

Answer:

If two vectors are perpendicular, then their dot product is zero.

Then (A+ 2B).(5A - 4B) = 0

=> A.5A + 2B.5A + A. (-4B) + 2B. (-4B) = 0

=> 5(|A|^2) + 10 A.B - 4A.B - 8(|B|^2) = 0

=> 5*1 +10|A||B| cos x - 4|A||B| cos x - 8*1 =0

[since A and B are unit vectors, x is the angle between vectors A and B]

=> 5 + 6|A||B| cos x - 8 =0

=> 6*1*1 cos x = 3

=> cos x = 1/2

=> x = 60° or 300°