Question

Here is question on an math assignment I was given, I have no clue what it is even asking.
It's a Challenge Yourself question, I've typed it exactly how it is on my paper:

A student is having difficult figuring out what is wrong with his proof:

Let C=D
C^2=CD
C^2 - D^2 = CD - D^2
(C - D)(C + D) = D(C - D)
C + D = D
However C=D
D + D = D
2D = D
2 = 1 ???

Answer 1

If C=D, C-D=0 and you cannot divide by zero.

Answer 2

Oh I get it now! Thanks