Evaluate `cos 48^(@) cos 42^(@) - sin48^(@) sin 42^(@)`

Explanation

`= Cos48^(@)cos42^(@)- Sin 48^(@)Sin 42^(@)`
`= Sin (90^(@)- 48^(@)) sin (90^(@)- 42^(@)) - Sin48^(@) Sin 42^(@)`
`= Sin 42^(@) Sin 48^(@)- Sin 48^(@) Sin 42^(@) =0`