For the curve with equation y = arsinh (x + 1), find
(a) the coordinates of its point of inflexion P
(b) an equation of the normal to the curve at P.
For (a), I know that if dy/dx = 0 and d^2 y/dx^2 = 0, but d^3 y/dx^3 ≠ 0, then the point is a point of inflexion. But now how can I start to solve this?
For (b), after finding P, it may be easy.