微分方程 differential equation
Ex:
dydx=f(x)\frac{dy}{dx} = f(x)dxdy=f(x)
y=∫f(x)dxy= \int f(x) dxy=∫f(x)dx
solved substitution
Ex2:
(ddx+x)(\frac{d}{dx}+x)(dxd+x)为annihilation operator 湮没算符 in quantum mechnics
dydx=−xy\frac{dy}{dx} = -xydxdy=−xy
dyy=−xdx\frac{dy}{y} = -xdxydy=−xdx
∫dyy=−∫xdx\int \f
