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Does .9999999… = 1?

February 19th, 2007 · 1 Comment

Apparently there is a lot of discussion out there as to the validity of this statement. The main argument for equality goes something like this. Say x = 0.99999… (or commonly expressed as .9). Multiply both sides by 10 and you have 2 equations that you can subtract from each other.

 10x = 9.9999999...
-  x = 0.9999999...
-------------------
  9x = 9

Reduce the result and now you have x = 1, but as we expressed earlier, x = 0.99999, so 0.99999… = 1. Simple enough, right?

Check out all of the discussion here, here, and and some false counter-examples here.

Tags: Math

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