Which statement is correct?

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?

You earn a 12% commission for every car you sell. how much is your commission if you sell a $23,000 car?

Which equation represents a direct linear variationa. y=x2b. y=2/5xc. y=1/xd. y=x+3