# Math Help - lagrange interpolation polynomial

1. ## lagrange interpolation polynomial

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

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?

2. ## Re: lagrange interpolation polynomial

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