令a=log0.5(x)则√(a²+4²)≥5a²≥9所以log0.5(x)≤-3，log0.5(x)≥3因为log0.5(x)是减函数所以x≥0.5^-3=8，x≤0.5^3=1/8且真数x>0所以0
