We simplify 1/(sqrt2+sqrt7)1√2+√7 by rationalizing the denominator i.e. multiplying numerator and denominator by conjugate of denominator.
As (sqrt2+sqrt7)(√2+√7) can be written as (sqrt7+sqrt2)(√7+√2) and its conjugate is (sqrt7-sqrt2)#, hence
1/(sqrt2+sqrt7)=1/(sqrt7+sqrt2)1√2+√7=1√7+√2
= (1xx(sqrt7-sqrt2))/((sqrt7+sqrt2)(sqrt7-sqrt2))1×(√7−√2)(√7+√2)(√7−√2)
= (sqrt7-sqrt2)/(7-2)=(sqrt7-sqrt2)/5√7−√27−2=√7−√25