(1) 令u=x^2-8x+15
f(x)=f(u)u∈[3,8]
所以,x^2-8x+15∈[3,8]
解得定义域x∈[1,7]
(2)由题意得,1-x^2≥0解得-1≤x≤1
x^2-1≥0解得x≤-1或1≤x
求交集解得x=1或-1