If `veca+vecb+vecc =0, |veca|=3, |vecb|=5, |vecc|=7` then the angle between `veca and vecb` is :

Options

A. `pi/2`
B. `pi/3`
C. `pi/4`
D. `pi/6`

Answer

B

Explanation

Let `theta` be the angle between `veca` and `vecb`
Then `angleC=pi-theta`
`therefore cos(pi-theta) = (3^(2)+5^(2)-7^(2))/(2(3)(5))`
`therefore -costheta=-1/2`
`therefore theta=60^(@)`