If vectors `vecP, vecQ and vecR` have magnitudes 5, 12 and 13 units and `vecP + vecQ = vecR`, the angle between `vecQ and vecR` is :

Options

A. `cos^(-1)(5/12)`
B. `cos^(-1)(5/13)`
C. `cos^(-1)(12/13)`
D. `cos^(-1)(2/13)`

Answer

C

Explanation

Here `P^(2) + Q^(2) = R^(2)`
`(5)^(2) +(12)(2) = (13)^(2)`
`:.` Angle between P and Q = `90^@`
Let `alpha` be the angle between Q and R.
`:.cosalpha = (12/13) " or " alpha = cos^(-1) (12/13)`