Question 96730
{{{(9+sqrt(5))(9-sqrt(5))}}} Start with the given expression



{{{81+9*sqrt(5)-9*sqrt(5)+sqrt(5)sqrt(5)}}} Foil



{{{81+9*sqrt(5)-9*sqrt(5)+5}}} Multiply



{{{81+cross(9*sqrt(5)-9*sqrt(5))+5}}} Cancel out like terms


{{{86}}} Combine like terms