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#9db06a02-ef28-4db8-b3aa-719be0e92a12简单填空题对数与对数函数函数

21. 设函数f(x)={2x,x1log2x,x>1f(x)=\left\{\begin{array}{l}{{2}^{-x},x\leqslant 1}\\ {lo{g}_{2}x,x>1}\end{array}\right.,则满足f(x)2f(x)\leqslant 2xx的取值范围是((  ))