If vector `P, Q and R` have magnitude 5,12,and 13 units and `vec(P)+vec(Q)=vec(R )`, the angle between Q and R is

Options

A. `coc^(-1) 5/(12)`
B. cos^(-1) 5/(13)`
C. cos^(-1) (12)/(13)`
D. cos^(-1) 7/(13)`

Answer

C

Explanation

Since, ` 5^2 + 12^2 = 13^2 = 13^2i.e P^2 = Q^2 . It means
` vec P` is perpendicular to ` vec Q`. If ` theta` is the angle between ` vec Q ` and ` vec R` then `cos theta = Q //R= 12 //13`
.