Trick/Fake proof of 2x2=5 ; algebraic form

Question

Just ran into "algebraic proof" that 2x2=5 on youtube. They didn't hide that it was a trick. Can't find where is the mistake.

Let a=4, b=5, c=1

1. c=b-a /multiply by (b-a)

2. c(b-a) = (b-a)(b-a) /distribute

3. cb-ca = b^2-2ab+a^2 /subtract a^2

4. cb-ca-a^2 = b^2-2ab /add ab

5. ab+cb-ca-a^2 = b^2-ab /subtract cb

6. ab-ca-a^2 = b^2-ab-cb /factor a and b respectively

7. a(b-c-a)=b(b-a-c) /divide by (b-a-c)

8. a=b /substitute with given value

9. 4=5

Answer 1

You can't divide by $b−a−c=5−4−1=0$. Theese kind of proofs always end up with a $0$-division and you can say that this is a good motivation you can't divide a number by $0$!