问题
填空题
已知函数f(x)对任意x，y∈R都有f(x＋y)＝f(x)＋f(y), 且f(2)＝4,则f(－1)＝____________.
答案
-2
f(0＋0)＝f(0)＋f(0), f(0)＝0，f(-1＋1)＝f(-1)＋f(1)=0，f(1＋1)＝f(1)＋f(1)=4
f(1)＝2, f(1)＝-f(1)=-2
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已知函数f(x)对任意x，y∈R都有f(x＋y)＝f(x)＋f(y), 且f(2)＝4,则f(－1)＝____________.
-2
f(0＋0)＝f(0)＋f(0), f(0)＝0，f(-1＋1)＝f(-1)＋f(1)=0，f(1＋1)＝f(1)＋f(1)=4
f(1)＝2, f(1)＝-f(1)=-2