Question

The range of the function f(x) = x + 5 is {7, 9}. What is the function’s domain?

{2, 4}
{-2, -4}
{12, 14}
{-12, -14}
{0, 5}

Answer 1

f(x) = x+5 is the same as y = x+5

Plug in y = 7 and solve for x
y = x+5
7 = x+5
7-5 = x+5-5
2 = x
x = 2
So x = 2 is part of the domain

Now plug in y = 9 and solve for x
y = x+5
9 = x+5
9-5 = x+5-5
4 = x
x = 4
and x = 4 is also part of the domain

Therefore the domain is {2,4}