利用公式△y≈y'△x即y1-y0=y'(x1)(x1-x0)这里令y=cosx，x1=60°，x0=59°y1=cosx1=cos60°=1/2，y0=cos59°y'(x1)=-sinx1=-sin60°=-√3/2∴1/2-cos59°≈-(√3/2)(60°-59°)≈-(√3/2)π/180∴cos59°≈1/2+π√3/360≈0.515
