Regarding U-Substitution of an indefinite integral?

I am trying to integrate the integral cot(27x). I rewrote cot(27x) as cos(27x)/sin(27x). Set U = to sin(27x) which gives me a dx of cos(27x) this should cancel out the numerator in my integral and leave me with 1/U. which should be ln(sin(27x). Apparently this is incorrect. Can anyone help solve this problem?