1) 2/√7=?
2)2/√2+1=?

3) 3-√3/2√3=?
4)a-2/√a-2√2=?

2/√7=2.√7/√7.√7=2√7/72/(√2 +1)=2.(√2-1)/(√2+1)(√2-1)=2.(√2-1)/(2-1)=2(√2-1)(3-√3)/2√3=(3-√3)√3/2√3√3=(3√3-3)/2.3=3(√3-1)/6=(√3-1)/2(a-2)/(√a-2√2)=(a-2)(√a+2√2)/(√a-2√2)(√a+2√2)==(a-2)(√a+2√2)/(a-8), a≠8