The length of the subnormal of the curves y=a/2(e^x/a+e^-x/a) at any point is

A stone is thrown vertically up and height s reached in time t is given by the formula s=2t²+3t+1. The stone reaches the maximum height in time t =

If A, B, C, D are the lengths of normals to the curves 1.y=4x² at (-1, 4) 2. Y=x³+1 at (1, 2) 3. Y=x³/2-x at (1,1) 4. 2x²+3xy-2y²=8 at (2, 3) then the ascending order of A,B,C,D is