(1/2)sqrt(125)-sqrt(2)(sqrt(10)-sqrt(98))
sqrt(10)=sqrt(2*5)=sqrt(2)*sqrt(5)
sqrt(98)=sqrt(49*2)=7sqrt(2)
(1/2)*sqrt(125)-sqrt(2)*(sqrt(10)-sqrt(98))=
=(1/2)*5sqrt(5)-sqrt(2)*sqrt(2)*sqrt(5)+sqrt(2)*7sqrt(2)=
=(5/2)*sqrt(5)-2sqrt(5)+14=(1/2)sqrt(5)+14