lim(x→1) (sin(x-1))=0lim(x→1) (x^2+x-1)=1所以lim(x→1) (sin(x-1))/(x^2+x-1)=0
lim(x→1) (sin(x-1))/(x^2+x-1)=【lim(x→1) (sin(x-1)】/【lim(x→1)(x^2+x-1)】 =sin0/1 =0
原式=f(1+-0)=cos(x-1)/(2x+1)=1/3
