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If veca+vecb+vecc=vec0, |veca| = 3, |vec...

If `veca+vecb+vecc=vec0, |veca| = 3, |vecb| = 5, |vecc| = 7`, then angle between `veca` and `vecb` is : a. `(pi)/(2)` b. `(pi)/(3)` c. `(pi)/4` d. `(pi)/(6)`

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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