prove the following
( 1 + tanA . tanB )² + ( tanA - tanB )² = sec²A . sec² B
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(tanA−tanB)
2
+(1+tanAtanB)
2
=tan
2
A+tan
2
B−2tanAtanB+1+tan
2
Atan
2
B+2tanAtanB
=tan
2
A+tan
2
B+1+tan
2
(A)tan
2
(B)
=tan
2
(A)[1+tan
2
(B)]+[1+tan
2
(B)]
=(1+tan
2
(B))(1+tan
2
(A))
=sec
2
B.sec
2
A
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