So, if t = ax^2+bx
then, differentiate both side with respect to time (t)
dt/dt = 2ax.dx/dt + b.dx/dt
1 = 2axv + bv
v.(2ax + b) = 1
(2ax + b) = 1/v
Again differentiate both side with respect to time (t)
2a.dx/dt = -v -2 . dv/dt
2av = v -2 . acceleration
acceleration = -2av 3
Where V is the Velocity.