Let us say there are two natural numbers "L" and "R".
We performed eight operations on these two numbers as

Step-1: L = R
Step-2: L x L = R x L
Step-3: L^2 - R^2 = LR - R^2
Step-4: (L + R)( L - R) = R(L - R)
Step-5: L + R = R
Step-6: R + R = R
Step-7: 2R = R
Step- 8: 2 = 1

What is wrong here?

Step5 is Wrong.
We divided the two sides by (L-R).Since L = R which indicates that (L - R) = 0 and we cannot divide by zero.

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