Question

If |A|= 5 unit |B| = 5 unit and angle between A and B is 2pi3 then |A+B| = ?
where A and B are vectors

Answer 1

$$\begin{gathered} \mathrm{\theta }=\frac{2\mathrm{\pi }}{3} \\ ={120}^{\mathrm{o}} \\ \left|\overrightarrow{\mathrm{A}}+\overrightarrow{\mathrm{B}}\right|=\sqrt{{\mathrm{A}}^2+{\mathrm{B}}^2+2\mathrm{ABcos\theta }} \\ =\sqrt{5^2+5^2+2\left(5\right)\left(5\right)\cos {120}^{\mathrm{o}}} \\ =\sqrt{25+25+\left(2\times 25\times -\frac{1}{2}\right)} \\ =5\mathrm{units} \end{gathered}$$