1.f(x)=2x^-4+x^(1/2) 定义域 x≠0
2.f(x)=√8-(1/2)^x 8－(1/2)^x≥0 (1/2)^x≥2³ 2^(-x)≥2³ ﹣x≥3 ∴x≤-3
3.f(x)=log1/2(1-x) 1-x＞0 x＜1