# Word/notation for "swallowing constant"?

1. May 25, 2014

### HJ Farnsworth

Greetings,

I used to sit in on an astrophysics course, where during derivations the professor would often absorb all of the constants in a given expression into a single ever-changing constant at the front of the expression. E.g., for a trivial example, let $X$ be $3$ times the circumference of a circle of radius $r$ times the perimeter of a square of side length $l$, with $k$ the constant in front:

$X=kC(r)P(l)=krP(l)=krl$.

The constant $3$, the $2\pi$ from $C(r)$, and the $4$ from $P(l)$ are all absorbed into $k$.

Is there a common name for this kind of device, which in the title of this thread I just called a "swallowing constant"? Also, is there a common notation for it?

Thanks for any help that you can give.

-HJ Farnsworth

2. May 25, 2014

### HallsofIvy

Staff Emeritus
I would use the phrase you did: "absorbed into k". There is no special name for the constant into which other constants because there is nothing special about it.