∵a^2+b^2=c^2
∴(a/c)^2+(b/c)^2=1
∴a/c<1,b/c<1
∴当n>2时,
(a/c)^n+(b/c)^n
<(a/c)^2+(b/c)^2=1
从而得a^n+b^n<c^n