Evaluate ∫√x²-36dx

a. x/4√x²-36-9ln|x/6+√x²-36/6|+C
b. x/2√x-36-18ln|x/6+√x-36/6|+C
c. x/2√x²-6-18ln|x/6+√x²-6/6|+C
d. -x/2√x²-36+18ln|x/6-√x²-36/6|+C
e. x/2√x²-36-18ln|x/6+√x²-36/6|+C