dp/dt=ap+bp^2
dp/(ap+bp^2)=dt
dp/p(a+bp)=dt
通解t=∫dp/p(a+bp)=(1/a)∫(a+bp-bp)dp/p(a+bp)=(1/a)[∫dp/p-∫bdp/(a+bp)]=(1/a)[ln|p|-ln|a+bp|]+C