More that we've learned/remembered today
A function has an inverse if it passes both the vertical line test (VLT) and horizontal line test (HLT). The term for such a function is "one-to-one."
To verify two functions are inverses of each other, show 𝑓∘𝑔𝑥=𝑥 AND 𝑔∘𝑓𝑥=𝑥 
Sometimes we have to restrict the domain of a function to make it invertible (AKA "to make it one-to-one")
To find the inverse function equation, swap x and y, then solve for y.