If vectors P, Q and R have magnitude 5, 12 and 13 units and →P+→Q=→R, the angle between Q and R is
cos−1512
cos−1513
cos−11213
cos−1713
|→P|=5,|→Q|=12and|→R|=13cosθ=QR=1213∴θ=cos−1(1213)