>>11383297Lagrange interpolation formula is simple. You build up the function from indicator functions: f_i(x_i)=1 and f_i(x_j)=1 for all i!=j. Because F_i has roots x_j, you can write f_i(x)=Prod{i!=j}(x_x_j)K
Then K is determined by the condition f_i(x_i)=1
Then adding up the indicator functions with appropriate multiplicative constants you get your interpolating polynomial :)
