拉格朗日matlab验证拉格朗日中值定理对函数y=4x^3-5x^2+x-2在区间【0,1】上的正确性

clear;
clc;
y = sym('4*x^3-5*x^2+x-2'); %%%% y
y0 = subs(y,'x',0); %%%%% y(0)
y1 = subs(y,'x',1); %%%%% y(1)
d_y = diff(y); %%%%% y'
kesi = solve(d_y*(1-0)-(y1-y0)); %%%%% 解 y'(ξ)*(b-a)=f(b)-f(a)
%%%%% 接下来需要判断ξ是否是[0,1]之间 %%%%%%%%%%%
kesi = double(kesi)
for ii = 1:length(kesi)
if kesi(ii)>0&kesi(ii)