Question

If R^2 = A^2+ B^2 + 2AB cose, if IAI = IBI then value of magntitude of R is equivalent to :
(A)2AcosO. (B)AcosO/2. (C)2AcosO/2 (D)2BcosO/2

Answer 1

R^2 = A^2 + B^2 + 2ABcosO

magnitude of A = magnitude of B

so, R^2 = 2A^2 + 2A^2cosO

R = A(2+2cosO)^-1/2

R = A*(2*2*cos^2(O/2))

R = A*2*cosO/2 = 2AcosO/2