Respuesta :

The identities we'll use are

tan(-x) = -tan(x)
tan(x) = sin(x)/cos(x)

which allows us to say...

3*tan(-x)*cos(x)
3*(-tan(x))*cos(x)
-3*tan(x)*cos(x)
-3*(sin(x)/cos(x))*cos(x)
-3sin(x)

The final answer is -3sin(x)