<-- notice that the 3 must be inside parentheses
                as a coefficient of sin(x). That was an
                error you made.  That is, the 3 is squared
                along with the sin(x).  The way you had it
                the 3 was not squared as it should have been.  













Since the cosine is sometimes negative, but
the square root of its square when written with a
radical is never negative.  Therefore we must
put absolute value bars around the square root to
prevent it from ever being negative:

Answer 

Edwin