Derived from (DX) / (Dy) = 1 / y ': (d ^ 2x) / (Dy ^ 2) = - y' '/ (y') ^ 3 rt In addition, what does "d" mean here? Tongji 6 p.90 suddenly comes out with the derivative function expressed by D, and the concept of "d" has not been explicitly put forward What about (d ^ 3) x / D (y ^ 3)

Derived from (DX) / (Dy) = 1 / y ': (d ^ 2x) / (Dy ^ 2) = - y' '/ (y') ^ 3 rt In addition, what does "d" mean here? Tongji 6 p.90 suddenly comes out with the derivative function expressed by D, and the concept of "d" has not been explicitly put forward What about (d ^ 3) x / D (y ^ 3)

If dy / DX is denoted as y ', then the reciprocal of Y' = DX / dy = (d ^ 2x) / (Dy ^ 2) = D (1 / y ') / dy = (d (1 / y') / DX) * (DX / dy) / / at the same time * DX = (d (1 / y ') / DX) * (1 / y') / DX takes 1 / y 'as the dependent variable