Question

ajutor este urgent . urgenta .​

Answer 1

$\it 8-2\sqrt{15}=5+3-2\sqrt{15}=(\sqrt5)^2-2\sqrt{15}+(\sqrt3)^2=(\underbrace{\sqrt5-\sqrt3}_{>0})^2\\ \\ Analog,\ 8+2\sqrt{15}=(\sqrt5+\sqrt3)^2.\\ \\ (4-2\sqrt5)^2=(\underbrace{2\sqrt5-4}_{>0})^2\\ \\ \\ a=\sqrt5-3+\sqrt5+3-2\sqrt5+4=4\in\mathbb{Z}$