# Math formulas you figured out with no help **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [July 14, 2012, 7:39pm UTC](https://boards.straightdope.com/t/math-formulas-you-figured-out-with-no-help/628242 "2012-07-14T19:39:32Z")\ **Posts on this page:** 6\ **Page:** 3
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [July 25, 2012, 2:18pm UTC](https://boards.straightdope.com/t/math-formulas-you-figured-out-with-no-help/628242/41 "2012-07-25T14:18:00Z")
> [@Balance](#): > > Not a formula, but I unwittingly reinvented Newton’s Method approximation when I was a lad, and made small forays into limit theory and some related basic concepts of calculus before I found out what calculus was. I was a little disappointed when I reached my high school Intro to Calc class and found that someone had already done the interesting bits. In my first programming class, we did a program to find square roots using Newton’s Method. I figured out how to generalize it for cube roots, etc. But Calculus. Yeah. When I started Calc in college I got really irked. I should have seen some of the basics coming, it was all so easy and logical for things like polynomials. I should have thought of some of that on my own. (They had taught some Calc in high school when an older sib took it, but by my turn there was just advanced Trig type stuff. If I had been fed a little Calc, I could have come up with all sorts of stuff with all the free time in high school.) ---
**Author:** ![leahcim](https://avatars.discourse-cdn.com/v4/letter/l/b4bc9f/32.png) [@leahcim](https://boards.straightdope.com/u/leahcim)\ **Post date:** [July 25, 2012, 2:30pm UTC](https://boards.straightdope.com/t/math-formulas-you-figured-out-with-no-help/628242/42 "2012-07-25T14:30:46Z")
Back in the day, I derived the first and second-order terms of a particular asymptotic expansion of the hypergeometric function. The limit was in Abramowitz and Stegun, but the higher order terms were not, and I needed them. I was pleased with myself. ---
**Author:** ![bup](https://avatars.discourse-cdn.com/v4/letter/b/6bbea6/32.png) [@bup](https://boards.straightdope.com/u/bup)\ **Post date:** [July 25, 2012, 7:36pm UTC](https://boards.straightdope.com/t/math-formulas-you-figured-out-with-no-help/628242/43 "2012-07-25T19:36:18Z")
> [@Spectre\_of\_Pithecanthropus](#): > > From there it’s not hard to show that, for example, 3126[sub]DEC[/SUB] is divisible by 9 because the sum of its digits is. :dubious: ---
**Author:** ![Spectre\_of\_Pithecanthropus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spectre_of_pithecanthropus/32/12343_2.png) [@Spectre\_of\_Pithecanthropus](https://boards.straightdope.com/u/Spectre_of_Pithecanthropus)\ **Post date:** [July 25, 2012, 7:49pm UTC](https://boards.straightdope.com/t/math-formulas-you-figured-out-with-no-help/628242/44 "2012-07-25T19:49:46Z")
> [@bup](#): > > > [@](#): > > > > From there it’s not hard to show that, for example, 3126[sub]DEC[/sub] is divisible by 9 because the sum of its digits is. > > :dubious: Sorry, I was thinking of the rule of threes and got mixed up. ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [July 25, 2012, 9:56pm UTC](https://boards.straightdope.com/t/math-formulas-you-figured-out-with-no-help/628242/45 "2012-07-25T21:56:19Z")
After I found that my 1-cup measuring scoop didn’t fit into the oatmeal canister, I figured out that I could use the 1/2-cup measuring scoop twice. **Knead** English major ---
**Author:** ![Oukile](https://avatars.discourse-cdn.com/v4/letter/o/13edae/32.png) [@Oukile](https://boards.straightdope.com/u/Oukile)\ **Post date:** [July 26, 2012, 12:56pm UTC](https://boards.straightdope.com/t/math-formulas-you-figured-out-with-no-help/628242/46 "2012-07-26T12:56:10Z")
1+2+3+…+n = n.(n+1)/2, looking at the square tiles on the floor when I was middle school. [Previous page](https://boards.straightdope.com/t/math-formulas-you-figured-out-with-no-help/628242.md?page=2)