[tex]\text{L.H.S}\\\\=\sin^2 \theta \tan \theta + \cos^2 \theta \cot \theta+2\sin \theta \cos \theta \\\\\\=\sin^2 \theta \cdot \dfrac{\sin \theta}{\cos \theta} + \cos^2 \theta \cdot \dfrac{\cos \theta}{\sin \theta} + 2\sin \theta \cos \theta\\\\\\=\dfrac{\sin^3 \theta}{\cos \theta}+ \dfrac{\cos^3 \theta}{\sin \theta}+ 2\sin \theta \cos \theta\\\\\\=\dfrac{\sin^4 \theta + \cos^4 \theta}{\cos \theta \cdot \sin \theta}+ 2\sin \theta \cos \theta\\\\[/tex]
[tex]=\dfrac{(\sin^2 \theta)^2 + (\cos^2 \theta)^2 }{\cos \theta \sin \theta}+ 2\sin \theta \cos \theta\\\\\\=\dfrac{(\sin^2 \theta + \cos^2 \theta)^2-2\sin^2 \theta \cos^2 \theta}{\cos \theta \sin \theta}+ 2\sin \theta \cos \theta\\\\\\=\dfrac{1-2 \sin^2 \theta \cos^2 \theta}{\cos \theta \sin \theta}+ 2\ sin \theta \cos \theta\\\\\\=\dfrac{1-2\sin^2 \theta \cos^2 \theta+2\sin^2 \theta \cos^2 \theta}{\cos \theta \sin \theta}\\\\=\dfrac 1{\cos \theta \sin \theta}\\\\[/tex]
[tex]=\dfrac{\sin^2 \theta + \cos^2 \theta}{\sin \theta \cos \theta}\\\\\\=\dfrac{\sin^2 \theta}{\cos \theta \sin \theta}+\dfrac{\cos^2 \theta}{\cos \theta \sin \theta}\\\\\\=\dfrac{\sin \theta}{\cos \theta}+\dfrac{\cos \theta}{\sin \theta}\\\\\\=\tan \theta + \cot \theta\\\\=\text{R.H.S}\\\\\text{Proved.}[/tex]
