Use the fundamental identities to simplify the expression.

3tan (-x) cosx

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)