Suppose to the contrary: rational number + irrational number = rational number . . . . (*)
i.e. R1 + IR = R2
i.e. m/n + IR = r/s where m,n,r,s are integers
.: IR = r/s - m/n = (nr - ms)/ns = integer/integer (a rational number)
.: an irrational number is a rational number
This is a contradiction
Therefore initial proposition (*) cannot be correct.