Question

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

Answer 1

Solve for k for each value of the range, and you will obtain each value of k that may belong to the domain

1) k^2 +2k +1 = 25

k^2 + 2k -24 = 0

(k + 6)(k- 4) = 0
k + 6 = 0 ⇒ k = - 6

k - 4 = 0 ⇒ k = 4

2) k^2 + 2k + 1 = 64

k^2 + 2k - 63 = 0

(k +  9)(k -  7) = 0

k + 9 = 0 ⇒ k = -9
k - 7 = 0 ⇒ k = 7

Then the largest possible domain is {-9, -6, 4, 7}

You might exclude one from -6 and 4 but not both.

You might also exclude one from -9 and 7 but not both

Because with those sets you will obtain all the images that are in the range.