Which two points have an undefined slope?

Question

A. 

(-1,1) and (1,-1)

B. 

(-2,2) and (2,2)

C. 

(-3,-3) and (-3,3)

D. 

(-4,-4) and (4,4)

Answer 1

C. if two points have the same x coordinate, a line through them has undefined slope

slope = (y1-y2)/(x1-x2) =(3--3)/(-3--3) = -6/0, but you can't divide by zero. It's undefined.