Dy/dx represents the first derivative of y to x, where it is a function of t,

Dy/dx = y '(t)/x '(t) = g(t) (denoted as g(t))

d？ y/dx？ Represents the second derivative of y to x, that is, the derivative of dy/dx to x,

So d? y/dx？ = g '(t) / x '(t)

=[y ' '(t)x '(t)-y '(t)x ' '(t)]/[x '(t)]？ (formula)