Question

sin 42 sin 48 -cos 42 cos 48​

Answer 1

Step-by-step explanation:

$\sin(42) \sin(48) - \cos(42) \cos(48) \\ = \sin(42) \cos(42 ) - \cos(42) \sin(42 ) \\ = 0 \\ coz \: \: \: \: \: \sin( \alpha ) = \cos(90 - \alpha ) \\ and \: \cos( \alpha ) = \sin(90 - \alpha )$