Question
Prove the following identities: $\Big(\frac{1}{\sec^2\text{x}-\cos^\text{x}}+\frac{1}{\text{Cosec}^2\text{x}-\sin^2\text{x}}\Big)\sin^2\text{x}\cos^2\text{x}=\frac{1-\sin^2\text{x}\cos^2\text{x}}{2+\sin^2\text{x}\cos^2\text{x}}$

Answer

$\text{L.H.S}=\Big(\frac{1}{\sec^2\text{x}-\cos^2\text{x}}+\frac{1}{\text{cosec}^2\text{x}-\sin^2\text{x}}\Big)\sin^2\text{x}\cos^2\text{x}$
$=\Bigg(\frac{1}{\frac{1}{\cos^2\text{x}}-\cos^2\text{x}}+\frac{1}{\sin^2\text{x}-\sin^2\text{x}}\Bigg)\sin^2\text{x}\cos^2\text{x}$
$\Bigg(\frac{1}{\frac{1-\cos^4\text{x}}{\cos^2\text{x}}}+\frac{1}{\frac{1-\sin^4\text{x}}{\sin^2\text{x}}}\Bigg)\sin^2\text{x}\cos^2\text{x}$
$=\Big(\frac{\cos^2\text{x}}{(1-\cos^2\text{x})(1+\cos^2\text{x})}+\frac{\sin^2\text{x}}{(1-\sin^2\text{x})(1+\sin^2\text{x})}\Big)\sin^2\text{x}\cos^2\text{x}$
$\left(\begin{array}{c}\text{Using}1-\text{a}^4=1-(\text{a}^2)^2\\ =(1-\text{a}^2)(1+\text{a}^2)\end{array}\right)$
$=\Big(\frac{\cos^2\text{x}}{\sin^2\text{x}(1+\cos^2\text{x})}+\frac{\sin^2\text{x}}{\cos^2\text{x}(1+\sin^2)}\Big)\sin^2\text{x}\cos^2\text{x}$
$\left(\begin{array}{c}\text{Using }1-\cos^2\text{x}=\sin^2\text{x}\\\&1-\sin^2\text{x}=\cos^2\text{x}\end{array}\right)$
$=\Big(\frac{\cos^4\text{x}(1+\sin^\text{x})+\sin^4\text{x}(1+\cos^2\text{x})}{\sin^2\text{x}\cos^2\text{x}(1+\cos^2\text{x})(1+\sin^2\text{x})}\Big)\sin^2\text{x}\cos^2\text{x}$
$=\frac{\cos^4\text{x}+\sin^2\text{x}\cos^4\text{x}+\sin^4\text{x}+\cos^2\text{x}\sin^4\text{x}}{(1+\cos^2\text{x})(1+\sin^2\text{x})}$
$=\frac{(\cos^2\text{x})^2+(\sin^2\text{x})^2+2\cos^2\text{x}\sin^2\text{x}-2\cos^2\text{x}\sin^2\text{x}+\sin^2\text{x}\cos^4\text{x}+\cos^2\text{x}\sin^4\text{x}}{(1+\cos^2\text{x})(1+\sin^2\text{x})}$
$(\text{adding an subtracting }2\cos^2\text{x}\sin^4\text{x})$
$=\frac{(\cos^2+\sin^2\text{x})^2-2\cos^2\text{x}\sin^2\text{x}+\sin^2\text{x}\cos^2\text{x}(\cos^2\text{x}+\sin^2\text{x})}{1+\sin^2\text{x}+\cos^2\text{x}+\sin^2\text{x}\cos^2\text{x}}$
$=\frac{1^2-2\cos^2\text{x}\sin^2\text{x}+\sin^2\text{x}\cos^2\text{x}.1}{1+1+\sin^2\text{x}+\cos^2\text{x}}$
$=\frac{1-\sin^2\text{x}\cos^2\text{x}}{2+\sin^2\text{x}\cos^2\text{x}}$
$=\text{R.H.S}$
$\text{Proved}$

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