# Need a definite answer for approximately equalAugust 28, 2008 11:14 AM   Subscribe

Here's the deal: I've exhausted my neurons looking for some kind of answer to a mathematical symbol stumper. I'd love to know who invented, originated, or was the first individual to use the double-tilde (≈) as a means of expressing/denoting "approximately equal" in mathematics. I know that Robert-Recorde is supposed to have introduced the "equals" sign (=) in 1557. Any and all assistance is greatly appreciated. I await enlightenment.
posted by font_snob to Writing & Language (5 answers total) 3 users marked this as a favorite

I have a copy of this book at home. I will check later to see if it is mentioned.
posted by wittgenstein at 12:05 PM on August 28, 2008

Best answer: The use of the single tilde for geometrical similarity and the tilde & horizontal line for congruence is due to Leibniz (See also here).

But for a more definitive answer, A History of Mathematical Notations by Florian Cajori says that Greenhill first used the parallel wavy lines in 1892 (Google Books link; hopefully it works for others). You can see the Greenhill work via Google Books. The citations given in Cajori are correct, though Greenhill does not explain his notation that I can see, so he may not have actually been the first.
posted by jedicus at 12:13 PM on August 28, 2008 [1 favorite]

I haven't found approximation yet in this list but its long and covers a lot.

There are some references to the first uses of the word approximation, so that may lead you down the correct path.
posted by wavering at 1:16 PM on August 28, 2008

Greenhill first used the parallel wavy lines in 1892

Except that those are not wavy lines, they're jagged; check out page 303 (near the bottom). Interesting question!
posted by languagehat at 1:48 PM on August 28, 2008

oops; Beaten to it!
posted by wittgenstein at 9:12 AM on August 29, 2008

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