limx→0(f(x)/x^2)=5得到f(x)=5x^2+o(x^2),o(x^2)代表x^3或更高次的x项.因此limx→0f(x)=limx→0( 5x^2+o(x^2) ) =0limx→0(f(x)/x)=limx→0(5x^2+o(x^2))/x= limx→0( 5x+o(x) )=0.题目关键在于得到f(x)=5x^2+o(x^2...