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Two vectors m and n are defined by m=3i+4j and \(n =...

Two vectors m and n are defined by m=3i+4j and n=2ij. Find the angle between m and n.

A.

97.9°

B.

79.7°

C.

63.4°

D.

36.4°

Correct answer is B

m.n=|m||n|cosθ

(3i+4j).(2ij)=64=2

2=|(3i+4j)||(2ij)|cosθ

|3i+4j|=32+42=25=5

|2ij|=22+(1)2=5

2=5(5)(cosθ)

cosθ=255=0.085 

\theta = \cos^{-1} 0.1788 = 79.7°