1) Sin(40+A)cos(10+A)-cos(40+A)sin(10+A)

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Solution

Here,
= Sin (40 + A) Cos (10 + A) - cos (40 + A) Sin (10 + A)
As, sin A cos B - cos A sin B = sin (A - B)
so,
= sin (40 + A - 10 - A)
= sin 30
= 1/2 = RHS
Hence, proved.

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