(x2−y2)dx+2xydy=0 ⇒dxdy=2xyy2−x2 Let y=vx ⇒⇒⇒⇒dxdy=v+xdxdvv+xdxdv=2vx2v2x2−x2v+xdxdv=2vv2−1xdxdv=2v−v2−1v2+12vdv=−xdx After integrating, we get lnv2+1=−ln∣x∣+lncx2y2+1=xc As curve passes through the point (1,1), so 1+1=c⇒c=2 x2+y2−2x=0, which is a circle of radius one.