Why does the domain of the function f(x)=x^2-2have to be restricted in order create an inverse function? What is the domain of the inverse of f(x)?

In the xy-plane, if the parabola with equation passes through the point (-1, -1), which of the following must be true?

Expresa commuter train leaves downtown sation and travels at a average speed of 55 miles per hour towards the north side sation, which is 50miles away. thirty minutes later, express commuter train #7 leaves north side and travels at a average speed of 35miles per hour towards downtown sation. at the moment the two trains pass each other, how far(in miles) is train #12 from the downtown sation and how long(in minutes) has the #12 train been traveling

The cost of using a service is $0.25 per min. what equation correctly represents the total cost c, in dollars, for d days of use?