format long;
f=@(x)x-cos(x);
a=f(0.6)-f(0.7);
b=f(0.6)-f(0.8);
c=f(0.6)-f(0.9);
d=f(0.7)-f(0.8);
e=f(0.7)-f(0.9);
g=f(0.8)-f(0.9);
sum9=0.9*f(0.6)*f(0.7)*f(0.8)/c/e/g;
sum6=-0.6*f(0.9)*f(0.7)*f(0.8)/c/a/b;
sum7=0.7*f(0.6)*f(0.9)*f(0.8)/a/d/e;
sum8=-0.8*f(0.6)*f(0.7)*f(0.9)/b/d/g;
ans=sum6+sum7+sum8+sum9