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Question
(1+tanA tanB)2+(tanA  tanB)2sec2A sec2B= ___
Options:
A .  1
B .  -tan A
C .  2
D .  cot A
Answer: Option A
:
A
(1+tan A tan B)2+(tan A-tan B)2sec2Asec2B
=1+2tan A tan B+tan2Atan2B+tan2A2tan A tan B+tan2Bsec2Asec2B
=1+tan2Atan2B+tan2A+tan2Bsec2Asec2B
=1+tan2A+tan2B+tan2Atan2Bsec2Asec2B
=1(1+tan2A)+tan2B(1+tan2A)sec2Asec2B
=(1+tan2A)(1+tan2B)sec2Asec2B
=(sec2A)(sec2B)sec2Asec2B.(1+tan2θ=sec2θ)
=1

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