f(x)=（3^2x）-[(k+1)3^x]+2 = (3^x)^2 - (k+1)*(3^x) + 2 设 3^x = t f(t) = t^2 - (k+1)t + 2 x 属于 R 则 t > 0 题目转化为 :t>0 时,f(t) 恒为正值 f(t) = t^2 - 2*[(k+1)/2]x + [(k+1)/2]^2 - [(k+1)/2]^2 + 2 =...