Which function has an inverse that is a function? a. b(x) = x2 + 3 b. d(x) = –9 c. m(x) = –7x d. p(x) = |x|

I'm not 100% sure, but I would go with C. m(x) = -7x

Explanation:
Find the inverse of all the functions:
A. b(x) =  + 3
y =  + 3
x =  + 3
x - 3 = 
= y
This isn't a function.

B. d(x) = -9 
There isn't an inverse of this because there is no x variable, the graph is a straight line of y = -9.

D. p(x) = |x| 
The inverse of this is ±x, which is also not a function, so the only option is C.

The inverse of C is
(x) = -