2. Find all the solutions of each of the following diophantine equations
a) $x^{2}-y^{2}=8$
b) $x^{2}-4 y^{2}=40$
c) $4 x^{2}-9 y^{2}=100$.
2. a) $x= \pm 3, y= \pm 1$
b) no solution
c) $x= \pm 5, y=0 ; x= \pm 13, y= \pm 8$