1.
If y=tan⁡−1(1+a2x2−1ax)y = \tan^{-1} \left( \frac{\sqrt{1+a^2x^2-1}}{ax} \right), then (1+a2x2)y′′+2a2xy′(1 + a^2x^2)y'' + 2a^2xy' is equal to