# find all function

**URL:** <https://boards.straightdope.com/t/find-all-function/580213>\
**Category:** Factual Questions\
**Created:** [April 29, 2011, 8:56pm UTC](https://boards.straightdope.com/t/find-all-function/580213 "2011-04-29T20:56:39Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![yearatioabove](https://avatars.discourse-cdn.com/v4/letter/y/898d66/32.png) [@yearatioabove](https://boards.straightdope.com/u/yearatioabove)\
**Post date:** [April 29, 2011, 8:56pm UTC](https://boards.straightdope.com/t/find-all-function/580213/1 "2011-04-29T20:56:39Z")

</div>

find all function f in real

such that

f(m^2+f(n))-f(m).f(m)=n

---

<div class="post-metadata">

**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\
**Post date:** [April 29, 2011, 9:06pm UTC](https://boards.straightdope.com/t/find-all-function/580213/2 "2011-04-29T21:06:09Z")

</div>

> [@yearatioabove](#):
>
> find all function f in real
> 
> such that
> 
> f(m^2+f(n))-f(m).f(m)=n

You first.

---

<div class="post-metadata">

**Author:** ![Omphaloskeptic](https://avatars.discourse-cdn.com/v4/letter/o/bcef8e/32.png) [@Omphaloskeptic](https://boards.straightdope.com/u/Omphaloskeptic)\
**Post date:** [April 29, 2011, 9:25pm UTC](https://boards.straightdope.com/t/find-all-function/580213/3 "2011-04-29T21:25:12Z")

</div>

> [@yearatioabove](#):
>
> find all function f in real
> 
> such that
> 
> f(m^2+f(n))-f(m).f(m)=n

{ }

---

<div class="post-metadata">

**Author:** ![Manlob](https://avatars.discourse-cdn.com/v4/letter/m/96bed5/32.png) [@Manlob](https://boards.straightdope.com/u/Manlob)\
**Post date:** [April 29, 2011, 10:02pm UTC](https://boards.straightdope.com/t/find-all-function/580213/4 "2011-04-29T22:02:47Z")

</div>

f(n)=n

---

<div class="post-metadata">

**Author:** ![Omphaloskeptic](https://avatars.discourse-cdn.com/v4/letter/o/bcef8e/32.png) [@Omphaloskeptic](https://boards.straightdope.com/u/Omphaloskeptic)\
**Post date:** [April 29, 2011, 10:22pm UTC](https://boards.straightdope.com/t/find-all-function/580213/5 "2011-04-29T22:22:53Z")

</div>

> [@Manlob](#):
>
> f(n)=n

Ahh, you’re right, misread the problem. (I read the second term as f(m)f(n) instead of f(m)^2.)