Answer: d(x) = -4x
Explanation:
If you were to graph each of the answer choices, only y = -4x passes the horizontal line test. This is the key to having an inverse function. This is because we need each y output to match up with exactly one x input, and vice versa. When the x and y swap happens, we'll still have a function when all is said and done.
Something like y = x^2+2x doesn't pass the horizontal line test. An output like y = 0 pairs up with the inputs x = 0 and x = -2 at the same time. This means that when we find the "inverse" of this, we'll have x = 0 pair up with y = 0 and y = -2 at the same time.
