Question

prove cos(81°+A)=(sin90°-A)
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Answer 1

Cos ( 81 +theta ) = sin (9- theta )

angle of cos is = 81- theta

so,

LHS= sin {90- (81+ theta) } [ sin( 90- theta )= cos theta]

= sin ( 90-81- theta)

= sin ( 9 - theta )

RHS = sin (90- theta)

therefore, RHS =LHS

HENCE PROVED

Answer 2

Cos ( 81 +theta ) = sin (9- theta )
angle of cos is = 81- theta
so,
LHS= sin {90- (81+ theta) } [ sin( 90- theta )= cos theta]
= sin ( 90-81- theta)
= sin ( 9 - theta )
RHS = sin (90- theta)
therefore, RHS =LHS
HENCE PROVED