Know More About Worksheet on Real World Problems with Rational Number This contradiction arises because our assumption- 21/2 is rational is wrong. Thus, 21/2doesn't belongs to the set of rational numbers. Here, a & b are co-primes. b*(21/2)=a Squaring both sides- 2b2=a2. (1) =>2 divide a2. =>2 divides a. a=2c, let c be any integer. Now, substitute the value of ‘a’ from equation 1: =>2b2=4c2, =>2 divide b2 => 2 divide b =>a and b have at least 2 as common factor≠1.