令x=y=0
则x+y=x-y=0
所以f(0)+f(0)=2[f(0)]²
2f[f(0)]²-2f(0)=0
f(0)[f(0)-1]=0
f(0)=0,f(0)=1
如果题目里说f(0)≠0
则f(0)=1,否则就有两个解