令p = y'
则dy''/dx = d(dy/dx)/dx = dp/dx = pdp/dy
pdp/dy + yexp(-vx)=0
p^2 +y^2 * exp(-vx) =0
p = -y exp(-vx/2)
就是(1/y)dy = -exp(-vx/2) dx
lny = 2/v exp(-vx/2) +C
令p = y'
则dy''/dx = d(dy/dx)/dx = dp/dx = pdp/dy
pdp/dy + yexp(-vx)=0
p^2 +y^2 * exp(-vx) =0
p = -y exp(-vx/2)
就是(1/y)dy = -exp(-vx/2) dx
lny = 2/v exp(-vx/2) +C