Question

prove please
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Answer 1

Given LHS = cos 85 * sin 80.

Multiply with 2, we get

1/2(2 cos 85 sin 80).

We know that 2 cos A sin B = sin(A + B) - Sin (A - B)

1/2(sin (85 + 50) - sin (85 - 50))

1/2(sin 135 - sin 35)

1/2(sin(90 + 45) - sin 35)

1/2(cos 45 - sin 35)

$\frac{1}{2} ( \frac{1}{ \sqrt{2} } - sin 35)$

$\frac{1 - \sqrt{2} sin 35 }{2 \sqrt{2} }$


LHS = RHS.


Hope this helps!

Answer 2

Hope it will help you .