What is the initial hypothesis in proving the proposition, "if a,b∈Z, then a²−4b²=0" using the method of contradiction?

i. a,b∈Z and a²−4b²=0
ii. a,b∈R if and only if a²−4b²=0
iii. If a,b∈Q then a²−4b²=0
iv. If a,b∈R then a²−4b²=0
v. If a,b∈Z then a²−4b²>0