牛顿迭代法：
x(n+1)=x(n)-[9(x(n))^2-sinx(n)-1]/[18x(n)-cosx(n)].
取x(0)=0.5,
x(1)=0.405129911,
x(2)=0.392101462,
x(3)=0.391847004,
x(4)=0.391846907,
3次迭代已经得到四位近似值x=0.3918.
二分法:f(x)=9x^2-sinx-1.
f(0)=-1,f(1)=7.15853,f(0.5)=0.770577.
f(0.25)=-0.68490,
f[(0.25+0.5)/2]=f(0.375)=-0.10065,
f[(0.375+0.5)/2]=f(0.4375)=0.29898,
f[(0.375+0.4375)/2]=f(0.40625)=0.09018,
.
要13次左右才能得到四位近似值.