SIN x=\cos x\RIGHTARROW x=\pi /4\] If \[y=\sin x\Rightarrow {{\LEFT( \frac{dy}{dx} \right)}_{x=\pi /4}}=\frac{1}{\sqrt{2}}\] If \[y=\cos x\Rightarrow {{\left( \frac{dy}{dx} \right)}_{x=\pi /4}}=\frac{-1}{\sqrt{2}}\] \[\tan \theta =\frac{{{m}_{1}}-{{m}_{2}}}{1+{{m}_{1}}{{m}_{2}}}=2\sqrt{2}\Rightarrow \,\theta ={{\tan }^{-1}}(2\sqrt{2})\].