A famous proof by contradiction is that the square root of 2 is an irrational number, i.e. it can't be written as a quote of two whole numbers.
In one of my books you're asked to show that the square...
@nprofile1q... Yes. More generally the square root of a positive integer is either a positive integer or it is irrational. So, for example, √30 is irrational because 5² < 30 < 6².