log2[4(1+a)/a]（x²）*[2a/(a+1)]^2x*[(a+1)^2/4*a^2]]大于0
4(1+a)/a]（x²）*[2a/(a+1)]^2x*[(a+1)^2/4*a^2]大于1
a属于[-1/3,1]答案a属于[-1/3,1]