令f(x)=0.9的x次方-2/21X,f(5)=0.11430,f(6)=-0.03999,所以根在{5,6】之间,取【5,5.5】验证,f(5.5)>0,故根在【5.5,6】中,再验证【5.5,5.75】,f(5.75)