Question

Sin 20.sin 10 as sum or difference

Answer 1

see explanation

Explanation:

The difference identity for the product is

sinxsiny =
`(1)/(2)` [ cos(x - y) - cos(x + y) ], thus

sin20sin10

=
`(1)/(2)` [ cos(20 - 10) - cos(20 + 10) ]

=
`(1)/(2)` ( cos10 - cos30 )