What can cause a rational function to be undefined at certain x-values ?

Which of the following is correct interpretation of the expression -4+13

Click an item in the list or group of pictures at the bottom of the problem and, holding the button down, drag it into the correct position in the answer box. release your mouse button when the item is place. if you change your mind, drag the item to the trashcan. click the trashcan to clear all your answers. solve this quadratic equation using the quadratic formula. 2x2 - 2x=1 need asap

Find the distance from the theater to the library. leave your answer in simplest radical form if necessary. 12 √12 74 √74