#color(red)(sqrt(50))=sqrt(5^2*2)=sqrt(5^2)*sqrt(2)=color(red)(5sqrt(2))#
#color(green)(sqrt(98))=sqrt(7^2*2)=sqrt(7^2)*sqrt(2)=color(green)(7sqrt(2))#
#color(red)(sqrt(50))-color(green)(sqrt(98))=color(red)(5sqrt(2))-color(green)(7sqrt(2))=(5-7)sqrt(2)=color(blue)(-2sqrt(2))#