prove tanA+ cotA = 2cosec2a
CotA- tanA = 2cot2A
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Answered by
24
tan(A) + cot(A) = 2 cosec(2A)
LHS
= tan(A) + cot(A)
= sin(A)/cos(A) + cos(A)/sin(A)
= [sin²(A) + cos²(A)]/[sin(A) cos(A)]
= 1/[sin(A) cos(A)], since sin²(A) + cos²(A) = 1
= 1/[(1/2) sin(2A)], from the identity sin(2A) = 2 sin(A) cos(A)
= 2/sin(2A)
= 2 cosec(2A)
= RHS
(2)..
cos A . sin A
-------- - --------
sin A . . cos A
cos^2 A - sin^2 A
--------------------------
. sin A . cos A
cos 2A
---------------
0.5sin 2A
2cot 2A
LHS
= tan(A) + cot(A)
= sin(A)/cos(A) + cos(A)/sin(A)
= [sin²(A) + cos²(A)]/[sin(A) cos(A)]
= 1/[sin(A) cos(A)], since sin²(A) + cos²(A) = 1
= 1/[(1/2) sin(2A)], from the identity sin(2A) = 2 sin(A) cos(A)
= 2/sin(2A)
= 2 cosec(2A)
= RHS
(2)..
cos A . sin A
-------- - --------
sin A . . cos A
cos^2 A - sin^2 A
--------------------------
. sin A . cos A
cos 2A
---------------
0.5sin 2A
2cot 2A
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