posted by Cam .
Find the second derivative of the function
probably a type, f(x) should be f(t)
f ' (t) = t^2 (-2)e^(-2t) + 2t (e^(-2t))
= -2t e^(-2t) (t-1)
= (2t - 2t^2) e^(-2t)
now use the product rule again and simplify similar to what I did above