Creating a class to extend Math

i have a function that i wrote in flash mx, and now that i’m using flash mx 2004, i’m going to have to use a class.

the function is like this:

//as 1.0:
function formatNumber(numberToFormat, decimalPlaces) {
//
}

how would i format that to put it into a class that extends the Math setion of as 2.0?