Question

If |$\overset{\rightarrow}{A}$+$\overset{\rightarrow}{B}$| = |$\overset{\rightarrow}{A}$| = |$\overset{\rightarrow}{B}$|, then the angle between $\overset{\rightarrow}{A}$and $\overset{\rightarrow}{B}$is-

• A. (a) $90^{0}$
• A. (b) $120^{0}$
• A. (c) $0^{0}$
• A. (d) $60^{0}$

Answer 1

(d)

|$\overset{\rightarrow}{A}$+$\overset{\rightarrow}{B}$| =$\sqrt{A^{2} + B^{2} + 2AB\cos\theta}$

Let here |$\overset{\rightarrow}{A}$+$\overset{\rightarrow}{B}$| = |$\overset{\rightarrow}{A}$| =$\overset{\rightarrow}{B}$| = R

So R² = R² + R² + 2R² cosq