Mathematics

Problem

Which expression gives the magnitude

R

of the resultant of two vectors of magnitudes

P

and

Q

making an angle

\theta

with each other? a)

R = \sqrt{P^{2}+Q^{2}+2PQ\sin\theta}

R = \sqrt{P^{2}+Q^{2}+PQ\cos\theta}

R = \sqrt{P^{2}+Q^{2}+2PQ\cos\theta}

R = \sqrt{P^{2}+Q^{2}-2PQ\cos\theta}