An alternating current is given by the equation $\mathrm{i}={\mathrm{i}}_1\mathrm{cos\omega }\mathrm{t}+{\mathrm{i}}_2\mathrm{sin\omega }\mathrm{t}$. The r.m.s. current is given by

• A

  $\frac{1}{\sqrt{2}}({\mathrm{i}}_1+{\mathrm{i}}_2)$

• B

  $\frac{1}{\sqrt{2}}{({\mathrm{i}}_{\mathrm{i}}+{\mathrm{i}}_2)}^2$

• C

  $\frac{1}{\sqrt{2}}{({\mathrm{i}}_1^2+{\mathrm{i}}_2^2)}^{1/2}$

• D

  $\frac{1}{2}{({\mathrm{i}}_1^2+{\mathrm{i}}_2^2)}^{1/2}$