Question

Given that $\vec{A}+\vec{B}=\vec{R}$ and $A^2+B^2=R^2$. The angle between $A$ and $B$ is

• A. 0
• B. $\pi /4$
• C. $\pi /2$
• D. $\pi$

Answer 1

Answer: (C)

$cos\theta =\frac{R^2-A^2-B^2}{2AB}=\frac{R^2-R^2}{2AB}=0$
$\therefore \theta =\pi /2$