Question

The range of the function f(k) = k2 + 2k + 1 is {25, 64}. What is the function’s domain?

Answer 1

f(k) = k2 + 2k + 1 = (k+1)^2
The range is what the function gives to you f(k)=25=5^2 or (-5)^2
f(k)=64=8^2 or (-8)^2

You need to find the k values for these boundary values to find the domain. 
Good luck :)