1. Find all the solutions of each of the following diophantine equations
a) $x^{2}+3 y^{2}=4$
b) $x^{2}+5 y^{2}=7$
c) $2 x^{2}+7 y^{2}=30$.
1. a) $x= \pm 2, y=0 ; x= \pm 1, y= \pm 1$ b) no solution c) $x= \pm 1, y= \pm 2$