Adrian's cd player can hold six disks at a time and shuffles all of the albums and their songs. if he has thirteen cd's, how many different combinations of six cd's can he put in the player?

One expression below in undefined, and the other expression has a well defined value. which expression is undefined and explain why it has no value. which expression is defined? what is the value of that expression and how do you know? what is a different expression using a trig inverse function that is also undefined?

Add the fractions, and simply the result to lowest terms. 2/3 + 2/7= ?

Just tell me how to set up the equation.