# A specific usage of "Solve" function

**URL:** <https://community.wolfram.com/t/a-specific-usage-of-solve-function/22781>\
**Category:** Questions\
**Tags:** algebra, equation-solving, symbolic-computations\
**Created:** [September 8, 2023, 1:58am UTC](https://community.wolfram.com/t/a-specific-usage-of-solve-function/22781 "2023-09-08T01:58:08Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![infei2006](https://avatars.discourse-cdn.com/v4/letter/i/ce73a5/32.png) [@infei2006](https://community.wolfram.com/u/infei2006)\
**Post date:** [September 8, 2023, 1:58am UTC](https://community.wolfram.com/t/a-specific-usage-of-solve-function/22781/1 "2023-09-08T01:58:08Z")

</div>

It is something from [https://mathematica.stackexchange.com/questions/114634/simplifying-polynomials-with-conditions-on-variables](https://mathematica.stackexchange.com/questions/114634/simplifying-polynomials-with-conditions-on-variables), that intend to minimize the number of variables. The problem is the usage of ``Solve". I know how to solve equations, like

```
Solve[x^2 + a x + 1 == 0, x]

```

However, for

```
Solve[pol == p + q + r - b && a + b == p + q + r, pol, {b, q, p, r}]

```

I am confused about “pol” and its position ``Solve[pol == p + q + r - b && a + b == p + q + r, ? , {b, q, p, r}]". I can not find any similar examples like this in the help document. How does it work? Is “pol” an expression or a variable? May I have more examples?

It is also posted at [https://mathematica.stackexchange.com/questions/289911/a-specific-usage-of-solve-function](https://mathematica.stackexchange.com/questions/289911/a-specific-usage-of-solve-function)