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It doesn't matter eight eighty

It doesn't matter eight eighty

Surely we have heard the expression many times “It doesn't matter eight eighty”.

Let's show it:

Let's call x = 80-8

Squared: x2=802-2·80·8+82

Substituting x2= x (80-8) = 80x-8x remains: 80x-8x = 802-2·80·8+82

Rearranging: 808-82-8x = 802-808-80x

Factoring: 8 (80-8-x) = 80 (80-8-x)

And dividing both sides of equality by (80-8-x) we have to 8 = 80!

Where this error?

Extracted from the page //www.acertijosypasatiempos.com

Solution

The mistake is that in the last step of development It is divided by the factor (80-8-x), which is equal to 0.
This is not valid because the division between 0 does not exist.