1. The problem statement, all variables and given/known data f(x) = Log(cosh(x-1)), find f'(x). 2. Relevant equations 3. The attempt at a solution f'(x) = [1/cosh(x) - 1] * d/dx [cosh(x) - 1], => f'(x) = sinh(x) / [cosh(x) - 1] Although, my marking scheme says the answer should instead be; cosh(x) + 1 / sinh(x). Can someone explain where I'm going wrong? Thanks.