Prove that

(i)

(ii)

(iii)

(i)

………[Using –2sinx.siny = cos(x + y)–cos (x–y)]

(ii)

………..[using 2cosx.cosy = cos(x + y) + cos(x–y)]

(iii)

...[Using2sinx.cosy = sin(x + y) + sin(x–y)]