PROVING METHOD OF CONTRADICTION WRONG:an excerpt from a book on method of contradiction:A proof that the square root of 2 is irrationalLet's suppose √2 is a rational number. Then we can write it √2 = a/b where a, b are whole numbers, b not zero.We additionally assume that this a/b is simplified to lowest terms, since that can obviously be done with any fraction. Notice that in order for a/b to be in simplest terms, both of a and b cannot be even. One or both must be odd. Otherwise, we could simplify a/b further.From the equality √2 = a/b it follows that 2 = a^2/b^2, or a^2 = 2 · b^2. So the square of a is an even number since it is two times something.From this we know that a itself is also an even number. Why? Because it can't be odd; if a itself was odd, then a · a would be odd too. Odd number times odd number is always odd. Check it if you don't believe me!Okay, if a itself is an even number, then a is 2 times some other whole number. In symbols, a = 2k where k is this other number. We don't need to know what k is; it won't matter. Soon comes the contradiction.If we substitute a = 2k into the original equation 2 = a^2/b^2, this is what we get:2 = (2k)^2/b^22 = 4k^2/b^22*b^2 = 4k^2b^2 = 2k^2This means that b^2 is even, from which follows again that b itself is even. And that is a contradiction!!!WHY is that a contradiction? Because we started the whole process assuming that a/b was simplified to lowest terms, and now it turns out that a and b both would be even. We ended at a contradiction; thus our original assumption (that √2 is rational) is not correct. Therefore √2 cannot be rational.However,if√(4)=a/bconsider that a & b are coprimesa^2=4b^2a is divisible by 4.let k=4a16k^2=4b^24k^2=b^2b is divisible by 4thus,a & b are not coprimes as they are divisible by 4so √4 is irrational≠true