作等距分划，Xi=-5+ih,h=10/n,i=0,1,……,n,并对Runge给出的函数y=1/(1+x2)作Lagrange插值，取n=10,20计算插值多项式Pn(x)在x=4.8处的误差，并作分析

用Romberg外推法计算圆周率Π=∫4/(1+X2)dx,要求绝对误差限小于0.5×10-8-For the equidistant partition, Xi =- 5+ ih, h = 10/n, i = 0,1, ... ..., n, and Runge' s function is given y = 1/(1+ x2) for the Lagrange interpolation, calculated taking n = 10,20 interpolation polynomial Pn (x) at x = 4.8 at the error, and an analysis method with Romberg extrapolation pi Π = ∫ 4/(1+ X2) dx, demand absolute error limit of small at 0.5 × 10-8