y=x+x2−115+x−x2−115
dxdy=15x+x2−114(1+x2−1x)+15x−x2−114(1−x2−1x)
dxdy=15x+x2−114(x2−1x+x2−1)+15x−x2−114(x2−1x−x2−1)
dxdy=x2−115[x+x2−115−x−x2−115]
⇒ x2−1.dxdy=15[x+x2−115−x−x2−115]
⇒ x2−1x.dxdy+x2−1dx2d2y=15×x2−115y
⇒ xdxdy+(x2−1)dx2d2y=15x2−1×x2−115y=225y