√5/√20
(√2-√7)(√7+√2)
(3-√9)'2
(√8-1)'2

√5/√20= √(5/20)= √(1/4)=1/2=0.5(√2-√7)(√7+√2)= (√2)^2-( √7)^2=2-7=-5(3-√9)^2=(3-3)^2=0^2=0(√8-1)^2=(√8)^2-2(√8)+1=8-4√2+1=~2.2