原式=(log1/4 x)^2-2*log(1/4) x+5
=(log1/4 x-1)^2+4
由2≤x≤4,得
log1/4 4≤log1/4 x≤log1/4 2即
-1≤log1/4 x≤-1/2
-2≤log1/4 x-1≤-3/2
9/4≤(log1/4 x-1)^2≤4
25/4≤(log1/4 x-1)^2+4≤8
即值域为{y|25/4≤y≤8}
原式=(log1/4 x)^2-2*log(1/4) x+5
=(log1/4 x-1)^2+4
由2≤x≤4,得
log1/4 4≤log1/4 x≤log1/4 2即
-1≤log1/4 x≤-1/2
-2≤log1/4 x-1≤-3/2
9/4≤(log1/4 x-1)^2≤4
25/4≤(log1/4 x-1)^2+4≤8
即值域为{y|25/4≤y≤8}