1.

Prove that (1 + tan A – sec A) × (1 + tan A + sec A) = 2 tan A

Answer»

LHS = (1 + tan A – sec A) × (1 + tan A + sec A)

(x – y) (x + y) = x2 – y2 

here x = 1 + tan A 

y = sec A 

LHS = (1 + tan A)2 – (sec A)2

= 1 + tan2 A + 2 tan A – sec2

= sec2 A + 2 tan A – sec2 A (1 + tan2 A = sec2 A) 

= 2 tan A = RHS

Hence, proved.



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