# Nerdy Dopers: What equations are permanently burned into your brain? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [February 25, 2005, 3:57pm UTC](https://boards.straightdope.com/t/nerdy-dopers-what-equations-are-permanently-burned-into-your-brain/291890 "2005-02-25T15:57:46Z")\ **Posts on this page:** 12\ **Page:** 2
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [February 26, 2005, 9:19am UTC](https://boards.straightdope.com/t/nerdy-dopers-what-equations-are-permanently-burned-into-your-brain/291890/21 "2005-02-26T09:19:29Z")
PV= nRT. And I still remember what R equals. The square on the hypotenuse is equal to the sum of the squares on the other two sides. I have remembered that for over 20 years now. ---
**Author:** ![Mississippienne](https://avatars.discourse-cdn.com/v4/letter/m/d2c977/32.png) [@Mississippienne](https://boards.straightdope.com/u/Mississippienne)\ **Post date:** [February 26, 2005, 9:35am UTC](https://boards.straightdope.com/t/nerdy-dopers-what-equations-are-permanently-burned-into-your-brain/291890/22 "2005-02-26T09:35:05Z")
Asoiaf: R+l=j. :d ---
**Author:** ![Cardinal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardinal/32/4000_2.png) [@Cardinal](https://boards.straightdope.com/u/Cardinal)\ **Post date:** [February 26, 2005, 11:28am UTC](https://boards.straightdope.com/t/nerdy-dopers-what-equations-are-permanently-burned-into-your-brain/291890/23 "2005-02-26T11:28:25Z")
These help kids on the SAT: 1, 1, root 2 1, 2, root 3 ---
**Author:** ![nocturnal\_tick](https://avatars.discourse-cdn.com/v4/letter/n/3d9bf3/32.png) [@nocturnal\_tick](https://boards.straightdope.com/u/nocturnal_tick)\ **Post date:** [February 26, 2005, 12:23pm UTC](https://boards.straightdope.com/t/nerdy-dopers-what-equations-are-permanently-burned-into-your-brain/291890/24 "2005-02-26T12:23:08Z")
[COLOR=Black]You know some people could call this psychological torture. …the flashbacks… I did two A levels in Maths and one in Physics. It took a long while to block out the equations and it’s all been undone in a matter of seconds. This still haunts me… [Product Moment Correlation Coefficient](http://mathworld.wolfram.com/CorrelationCoefficient.html) :shudder: ---
**Author:** ![Strainger](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/strainger/32/244_2.png) [@Strainger](https://boards.straightdope.com/u/Strainger)\ **Post date:** [February 26, 2005, 4:38pm UTC](https://boards.straightdope.com/t/nerdy-dopers-what-equations-are-permanently-burned-into-your-brain/291890/25 "2005-02-26T16:38:18Z")
Stress engineer here: [symbol]s[/symbol]=Mc/I (bending stress at outer fiber) [symbol]s[/symbol]=P/A (axial stress) I=bh[sup]3[/sup]/12 (area moment of inertia for a rectangular x-section) I=[symbol]p[/symbol]r[sup]4[/sup]/4 (circular x-section) [K]{x}={F} (Hooke’s Law: foundation of finite element theory) ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [February 26, 2005, 8:37pm UTC](https://boards.straightdope.com/t/nerdy-dopers-what-equations-are-permanently-burned-into-your-brain/291890/26 "2005-02-26T20:37:49Z")
What’s burned into my brain goes far beyond mere equations. I have the standard constructions for **N** (in ZF and NGB!), **Z** , **Q** , **R** , **C** , etc. and their properties. In addition, I know the definition of a group, a field, a vector space, all other kinds of categories… Yeesh. I have to go back to school just so I can justify the contents of my head. ---
**Author:** ![Ringo](https://avatars.discourse-cdn.com/v4/letter/r/779978/32.png) [@Ringo](https://boards.straightdope.com/u/Ringo)\ **Post date:** [February 26, 2005, 10:36pm UTC](https://boards.straightdope.com/t/nerdy-dopers-what-equations-are-permanently-burned-into-your-brain/291890/27 "2005-02-26T22:36:57Z")
And I typoed the reflection coefficient: (ρ2_v2\*\*-\*\*ρ1_v1)/ρ2_v2+ρ1_v1) ---
**Author:** ![bitwise](https://avatars.discourse-cdn.com/v4/letter/b/ea5d25/32.png) [@bitwise](https://boards.straightdope.com/u/bitwise)\ **Post date:** [February 27, 2005, 10:55am UTC](https://boards.straightdope.com/t/nerdy-dopers-what-equations-are-permanently-burned-into-your-brain/291890/28 "2005-02-27T10:55:40Z")
a^phi(n) = 1 (mod n) where a is relatively prime to n (x+y)^n = sum(k, 0, n) C(n,k) x^k y^(n-k) f(A intersection f^(-1)(B)) = f(A) intersection B ---
**Author:** ![Antonius\_Block](https://avatars.discourse-cdn.com/v4/letter/a/51bf81/32.png) [@Antonius\_Block](https://boards.straightdope.com/u/Antonius_Block)\ **Post date:** [February 27, 2005, 12:23pm UTC](https://boards.straightdope.com/t/nerdy-dopers-what-equations-are-permanently-burned-into-your-brain/291890/29 "2005-02-27T12:23:54Z")
I’ve got about 20 in the cache, but my favorite’s already been mentioned a few times: > [@Stranger On A Train](#): > > Euler’s Identity: > **e[sup]_j_π[/sup] + 1 = 0** I always think of this as **e[sup]_i_π[/sup] = -1**. That way, whenever you knock on someone’s door, you can sing it to the tune of “_Shave and a haircut, two bits!_”: “ **Ee to the eye pie, equals minus one!** ” [I’m jealous of \*\*Hyperelastic\*\*'s arm tattoo, however.] ---
**Author:** ![ErinPuff](https://avatars.discourse-cdn.com/v4/letter/e/dbc845/32.png) [@ErinPuff](https://boards.straightdope.com/u/ErinPuff)\ **Post date:** [February 27, 2005, 1:31pm UTC](https://boards.straightdope.com/t/nerdy-dopers-what-equations-are-permanently-burned-into-your-brain/291890/30 "2005-02-27T13:31:39Z")
In seventh grade my algebra teacher told us to put the quadratic formula to a song to help us learn it. I discovered it went quite nicely to a song we were playing in band called “Sunset on the Sahara” that was supposed to sound vaguely Egyptian or something. For five years I couldn’t write the formula down without getting the damn song stuck in my head. It only let up because I stopped taking math. But now I have it in my head again. Augh. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [February 27, 2005, 5:28pm UTC](https://boards.straightdope.com/t/nerdy-dopers-what-equations-are-permanently-burned-into-your-brain/291890/31 "2005-02-27T17:28:46Z")
> [@ErinPuff](#): > > For five years I couldn’t write the formula down without getting the damn song stuck in my head. It only let up because I stopped taking math. But now I have it in my head again. Augh. No need to thank us. It’s all part of the service. 😃 Stranger ---
**Author:** ![Mariemarie](https://avatars.discourse-cdn.com/v4/letter/m/58f4c7/32.png) [@Mariemarie](https://boards.straightdope.com/u/Mariemarie)\ **Post date:** [February 28, 2005, 1:54am UTC](https://boards.straightdope.com/t/nerdy-dopers-what-equations-are-permanently-burned-into-your-brain/291890/32 "2005-02-28T01:54:11Z")
The minority carrier drift current is negligible. [Previous page](https://boards.straightdope.com/t/nerdy-dopers-what-equations-are-permanently-burned-into-your-brain/291890.md?page=1)