Anyone a fan of Heathers? If so, wanna be friends?

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?

In the figure shown below, m < 40 and ab =8. which equation could be used to find x?

Consider that lines b and c are parallel. what is the value of x? what is the measure of the smaller angle?