f(x)=log3((mx^2+8x+n)/(x^2+1)) 值域为[0,2]
所以0=log3((mx^2+8x+n)/(x^2+1)) =2
1=(mx^2+8x+n)/(x^2+1)=9
(1-m)x*x-8x-n+1=0
(9-m)x*x-8x+9-n=0
方程=0有唯一解 有△=0
64-4(1-m)(1-n)=0
64-4(9-m)(9-n)=0
1-m0 9-m0
所以解得m=5 n=5