Prove the following:
We know that: cos(x + y) = cosx cosy - sinx siny ...(i)
sin (x + y) = sinx cosy + cosx siny ...(ii)
...(iii)
...(iv)
Replacing x by and y by x in (i), we get
= sin x [By using (iii) and (iv)]
Hence,
Replacing x by and y by x in (ii), we get
= - cosx [By using (iii) and (iv)]
Hence,
Hence,