If f(x)=x−af(x) = \sqrt{x-a}f(x)=x−a and f−1(2)=6f^{-1}(2) = 6f−1(2)=6, find aaa.
a=1a = 1a=1
a=2a = 2a=2
a=−2a = -2a=−2
a=0a = 0a=0