lagrange interpolation polynomial

I have some difficulty understanding a step in the following solved problem on lagrange interpolating polynomials:

http://img846.imageshack.us/img846/3...olatingpol.png

So, in the 5th line of the working, how did they go from 1/2 to 4, and from 1/6 to 6? How did they change those?

Re: lagrange interpolation polynomial

Quote:

Originally Posted by

**demode** So, in the 5th line of the working, how did they go from 1/2 to 4, and from 1/6 to 6? How did they change those?

In $\displaystyle \mathbb{Z}_7$ we have $\displaystyle 2\cdot 4=1$ so $\displaystyle 1/2=4$ etc.