Question

1) (√7-√28)² 2) (5√2+2√5)(5√2-2√5)

Answer 1

$(\sqrt7-\sqrt28)^2=7-2\sqrt{7*28}+28=\\=7-2\sqrt{7*7*2*2}+28=7-2*7*2+28=7-28+28=7;\\\\(5\sqrt2+2\sqrt5)(5\sqrt2-2\sqrt5)=(5\sqrt2)^2-(2\sqrt5)^2=25*2-4*5=\\=50-20=30$