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The 2=1 puzzle

Dr Yan tests out a mathematical equation that seems to prove that 2=1. Or does it? Try the equation at home and see if you can spot the 'trick'?

a=b

[multiply both sides by a]

a×a = a×b

[add a×a to both sides]

a×a + a×a = a×a + a×b

[subtract 2×a×b from both sides]

a×a + a×a - 2×a×b = a×a + a×b - 2×a×b

[You can re-write this as following:]

2×a×a - 2×a×b = a×a - a×b

[This can then be represented as:]

2(a×a - a×b) = 1(a×a - a×b)

[Divide both sides by (a×a - a×b)]

2=1

Release date:

Duration:

5 minutes