calculus

1. s(t) = (1 / 3)t^3– t + 1 correct   

2. s(t) = t + sin(t) where s in meters and t in seconds find the acceleration at: t = Pi / 4; s correct 

3. d/dx (1+ sin^2x / x + tan^315x) change 

4. df ^-1 / dx for f(x) = x +3 / 2x + 5 at x = 3. change