5√2 + 23√27 - √98 = 5√2 + 23√(3^3) - √(27^2) =
= 5√2 + 233√3 - 7√2=
= 5√2 + 69√3 - 7√2=
= (5 - 7)√2 + 69√3 =
= -2√2 + 69√3.