1. The given equation can be written as dxdy=xy+y2y2
Put y=vx, then dxdy=v+xdxdv . The given equation becomes
v+xdxdvxdxdvv21+vdvv21dv+v1dv=vx2+v2x2v2x2=v+v2v2=1+vv−1=−1+vv2=−xdx=−xdxIntegrating both sides, we get−v1+logv−v1−v1−v1yxeyx∴y=−logx+logc=−logv−logx+logc=−(logv+logx−logc)=−log(cvx)=log(cy) (Using y=vx,v=xy)=cy=ceyx
2. The equation can be written as dxdy=x2y2−2xy
Put y=vx, then dxdy=v+xdxdv . The given equation becomes
v+xdxdvxdxdvv(v−3)dv=x2v2x2−2vx2=v2−2v=v2−3v=xdxUsing partial fractions for the term on LHS, we get31[v−3dv−vdv]=xdxv−3dv−vdv=3xdxIntegrating both sides, we getlog(v−3)−logvlog(vv−3)log(vv−3)vv−31−v31−y3xy3x∴y=3logx+logc=logx3+logc=log(cx3)=cx3 (taking anti-logarithms)=cx3=cx3 (Using y=vx)=1−cx3=1−cx33x
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