Determine wether the equation is an identity or not an identity

What is the inverse of the function f(x) = 2x + 1?

Assume that there is a 11% rate of disk drive failure in a year. a. if all your computer data is stored on a hard disk drive with a copy stored on a second hard disk drive, what is the probability that during a year, you can avoid catastrophe with at least one working drive? b. if copies of all your computer data are stored on four independent hard disk drives, what is the probability that during a year, you can avoid catastrophe with at least one working drive?

How can you find the magnitude of a vector, v = < x, y > , where the horizontal change is x and the vertical change is y?