Question

PROVE THAT:
cos (x+y).cos (x-y) = cos^2y - sin^2x​

Answer 1

Answer:

(Cos x cosy - sinxsiny) (cosxcosy+sinx siny)

=cos^2 xcos^2 y-sin^2 xsin^2 y

=(1-sin^2 x) cos^2 y-sin^2 x(1-cos^2 y)

=cos^y-sin^x

Answer 2

(Cos x cosy - sinxsiny) (cosxcosy+sinx siny)

=cos^2 xcos^2 y-sin^2 xsin^2 y

=(1-sin^2 x) cos^2 y-sin^2 x(1-cos^2 y)

=cos^y-sin^x

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