Given the parametric equations x=f(t),y=g(t). Then d2ydx2 equals
The second derivative of a single valued function parametrically represented by x=ϕ(t) and y=ψ(t), ( where ϕ(t) and ψ(t) are different functions and ϕ′(t)≠0) is given by
By introducing a new variable t, putting x=cos t , the expression is (1−x2)d2ydx2−xdydx+ytransformed into :