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Question
Prove the following identity :
(secA - cosA)(secA + cosA) = `sin^2A + tan^2A`
Solution
LHS = (secA - cosA)(secA + cosA)
= `(sec^2A - cos^2A) = 1 + tan^2A - (1 - sin^2A)`
= `tan^2A + sin^2A` = RHS
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