Please answer the following question

$$\begin{gathered} \mathbf{9}\mathbf{.} \mathrm{An} \mathrm{alternating} \mathrm{current} \mathrm{is} \mathrm{given} \mathrm{by} l = l_1 \mathrm{cos\omega t} + l_2 \mathrm{sin\omega t}. \mathrm{The} \mathrm{RMS}\hspace{0.17em}\mathrm{value} \mathrm{of} \mathrm{current} \mathrm{is} \mathrm{given} \mathrm{by} \\ \left(1\right) \frac{l_1 + l_2}{\sqrt{2}} \left(2\right) \frac{(l_1 + l_2{)}^2}{2} \\ \left(3\right) \sqrt{\frac{l_1^2 + l_2^2}{2}} \left(4\right) \frac{\sqrt{l_1^2 + l_2^2}}{2} \end{gathered}$$