f(a)=k
means
when you input a, in f(x), you get k
lets see
1., this is false, unless f(x)=x which is not always true
2. this is the inverse, this is the sme function but input and output are switched
f(a)=k turns to f⁻¹(k)=a
true
3. this is true only if f(x)=x
2 is the right answer
