1.y=(x²+2x+4)/x=x+2+4/x≥2+2√[x*(4/x)]=2+4=6当x=4/x,即x=2时取等号此时函数y=(x^2+2x+4)/x取最小值,为62.∵x>0∴y=x/(x²+x+1)>0∴当1/y取最小值时,y取最大值1/y=(x²+x+1)/x=x+1+1/x≥1+2√[x*(1/...