1. The problem statement, all variables and given/known data Find d2/dx2 0∫x (1∫sint√(1+u^4)du)dt 2. Relevant equations 3. The attempt at a solution Initially I treated this problem as the second derivative of a double integral and thus quickly found myself at the result cosx√1+sin4x, by the fundamental theorem of calculus. However I realized that the problem asks for the second derivative according to x, and now I think my solution is incorrect. Would the correct method be to solve the integral √(1+u^4)du, then do the derivatives?