If a vector A, B, C be te three vectors such that vector A+vector B+vector C=0 and mode of A=3, mode of B=5 and mode of C=7. Find the angle between A and B.
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Answer: Angle between A and B is 60.
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∣a∣=3,∣b∣=4,∣c∣=5
a+b+c=0
a+b=−c
∣a+b∣=∣−c∣
∣a+b∣^2 = I c I^2
I a I^2 + I b I^2 + 2ab = I c I^2
9+25+2a.b=49
Also ab=3×5
Hence 9+25+2abcosθ=49
15=30cosθ
Or cosθ= 1/2
θ= 60°
So angle is 60°
Explanation:
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