Q: Prove that there is no rational number whose square is 98

Here is what i have so far:

Suppose, for contradiction, that there is a rational number a/b with gcd(a,b)=1 whose square is 98.

(a/b)^2=98

a^2=98b^2

a^2=2(49)b^2

So, does this show that a is even? how do i show that b is even to get a contradiction?