分母因式分解x^2-9=x^2-3^2=(x-3)(x+3)原式=(x-3)/[(x-3)(x+3)]=1/(x+3)所以lim(x->3) 根号下[(x-3)/(x^2-9)]=lim(x->3) 根号下(1/(x+3))=根号(1/(3+3))=根号(1/6)=(根号6)/6
