Question

设函数f(x)对任意x,y满足f(x+y)=f(x)+f(y),且f(2)=4,则f(-1）=?答案为-2,

Answer 1

f(2)=f(1+1)=f(1)+f(1)=f(-1+2)+f(-1+2)=2f(-1)+2f(2)=4 所以2f(-1)=-4 所以f(-1)=-2