已知函数f(x)=x^2+2x+4,若x1+x2=0且x1
问题描述：
已知函数f(x)=x^2+2x+4,若x1+x2=0且x1
答
f(x1)-f(x2)
=x1²+2x1+4-x2²-2x2-4
=x1²-x2²+2(x1-x2)
=（x1-x2)(x1+x2)+2(x1-x2)
=(x1-x2)[(x1+x2)+2] （x1+x2=0)
=2(x1-x2)
∵x1