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Suppose veca + vecb + vecc = 0, |veca| =...

Suppose `veca + vecb + vecc = 0, |veca| = 3, |vecb| = 5, |vecc| = 7`, then the angle between `veca & vecb` is

A

`(pi)/(2)`

B

`(pi)/(3)`

C

`(pi)/4`

D

`(pi)/(6)`

Text Solution

Verified by Experts

The correct Answer is:
B

Let `theta` be the angle between a and b. then, `angleC=pi-theta`.
`thereforecos(pi-theta)=(3^(2)+5^(2)-7^(2))/(2(3)(5))`
`therefore-costheta=(-1)/(2)`
`thereforetheta=60^(@)=(pi)/(3)`
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