Question

Without using trigonometric table prove that (1) cos 81º - sin 9º =0​

Answer 1

sin9° can be written as sin(90°-81°)

and

sin(90°-theta) = cos (theta)

so,

sin(90°-81°) = cos 81°

thus according to question,

=> cos81° - sin9°

=> cos81° - cos81°

= > 0

Answer 2

Answer : = LHS = cos 81 degree -sin 9 degree = 0

= cos [ 90^circ-9^circ]-sin9^circ

=sin 9^circ - sin 9^ circ

=0

=RHS

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