Hi. Stuck on this substitution. The integral is

(x (cos(x/3))^(-1))/(9-x^2)^(1/2)

The substitution is x=3cos(u)

After performing the substitution the answer gives

the integral.

(3cos(u) u - 3sin (u) du)/3 sin (u)

I arrived here OK, however it states that the above tidies to

-3 u cos(u) du

Stuck here on how it tidies to this

Thanks