Question

prove sin a = cos a where a + b = 90

Answer 1

sina = cosb
implies sina=sin(90-b)
imples a=90-b
there fore a+b=90

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Answer 2

Given - a+b=90
so, a=90-b

solving for lhs
sin a= sin(90-b)
= cos b

this the right thing that can be proved.
hope it helps.
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