y(x + y + 1) dx + (x + 2y) dy = 0:运用正合方程式求解

由题意设M(x,y)=y(x + y + 1),N(x,y)= (x + 2y),下述中a为偏导则由此方程的正合可以知道有：a[M(x,y)]/ay=x+2y+1,a[N(x,y)]/ax=1即有x+2y+1=1,即x+2y=0又 ∫N(x,y)dx=y^2+xy+V(x)则有y(x + y + 1) =a[y^2+xy+V(x)]/a...