f(x)=a(log2X-log2(8))(log2(4)+log2x)=a((log2x)^2-log2x-6)
設(shè)t=log2x,那么f(t)=a(t^2-t-6),t的取值范圍為：[-3,2]
顯然g(t)=t^2-t-6的對(duì)稱軸方程為t=1/2,令t=log2x=1/2求得x=√2
且a≠0,當(dāng)a>0時(shí),則t=-3,或2時(shí),函數(shù)有最大值為25,
此時(shí)當(dāng)t=2時(shí),代入求得a=-25/4,不合假設(shè),設(shè)去.
當(dāng)t=-3時(shí),代入求得：a=25/6,此時(shí)x=1/8
當(dāng)a