(√2+3) - (√2-5) Let the 2nd bracket open by minus. Then we'll get... √2+3-√2+5 From this, we can cancel √2 and -√2. It is because the sign of the first √2 is + and second √2 is -. [Eg: +1-1=0] Therefore, we'll get 3+5 = 8, which is a rational number.