Just reading through a proof which states that:

dy/dt=(-2x^-3)(dx/dt)

Then it states that:

d2y/dt2= (-2x^-3)(d2x/dt2)+(6x^-4)(dx/dt)^2

I can see that the chain rule is used, although I do not understand why the last dx/dt is squared - could somone explain how the first equation transforms to the next please,

Many thanks,

Bryn