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3 years ago

Cos xcos y=1/2(sin(x+y)+ sin(x-y))

Mathematics

1 answer:

garri49 [273]3 years ago

7 0

Taking Rhs

1/2 [sin(x+y)+ sin (x-y)]

using sinA + sin B = 2 cos (A+B)/2 cos( A - B)/2

1/2 [ 2 Cos ( x+y+x-y)/2 . Cos (x+y-x+y)/2]

=Cos 2x/2. Cos 2y/2 = Cos x . Cos y

Hence true

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