Question
Prove that the following identities:
Sec A( 1 + sin A)( sec A - tan A) = 1.

Answer

LHS = sec A(1 + sin A )( sec A - tan A)
$=\frac{1}{\cos A}(1+\sin A)\left(\frac{1}{\cos A}-\frac{\sin A}{\cos A}\right)$
$=\frac{1}{\cos A}(1+\sin A)\left(\frac{1-\sin A}{\cos A}\right)$
$=\frac{1-\sin ^2 A}{\cos ^2 A}=\frac{\cos ^2 A}{\cos ^2 A}$
= 1
= RHS
Hence proved.

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