令p=y"
则y"'=dp/dx
代入得：dp/dx* p=a
pdp=adx
2pdp=2adx
p^2=2ax+c1
y"=√(2ax+c1)
积分：y'=1/(3a)* (2ax+c1)^(3/2)+c2
再积分：y=1/(15a^2)*(2ax+c1)^(3/2)+c2x+c3