Question

Where is the logical flaw?

a=b
a+a=a+b
2a=a+b
2a-2b=a-b-2b
2(a-b)=a-b
2=1

Answer 1

fourth line, I think

Answer 2

a-b=0
You can't divide by zero

Answer 3

in the last step you divide both sides by (a-b) but because a=b, a-b=0 and you can't divide by 0

Answer 4

in fourth line isn't that: 0 = negative number

Answer 5

there looks to be a typo in line 4 also
you should have 2a-2b=a+b-2b

which gives you 2a-2b=a-b

Answer 6

I think that's where the logical flaw is

Answer 7

With that typo there are two logical flaws

Answer 8

4th line a+b becomes a-b

Answer 9

then division by zero