x=tcost & y=t+sint then find dx2/d2y

Answer 1

The symbol
dx2/d2y
doesn't make sense.

Do you want d/dy (dx/dy) = d^2x/dy^2 ?

You can get dx/dy parametrically in terms of t using

dx/dy = (dx/dt)/(dy/dt)

After that, you can use the chain rule for d^2/dy^2. It will still be in terms of t.