Question

We can prove 1=2
proof: a=b
a square = ab
a sq -b sq = ab-b sq
(a-b)(a+b)=b(a-b)
a+b = b
b+b =b
2b=b
2=1
but fundamentally it is wrong

Answer 1

proof: a=b
a square = ab
a sq -b sq = ab-b sq
(a-b)(a+b)=b(a-b)

we cannot cancel (a-b) from both sides , because its given a=b
Therefore we know that a-b=0
and we cannot cancel zeroes from lhs and rhs