当x当x当x当x
当x当xy=1-x+1/(5-4x)=(5-4x)/4+1/((5-4x)-1/4由于x0这样,(5-4x)/4+1/((5-4x)≥2*根号下[(5-4x)/4*1/((5-4x)]=4所以,y=1-x+1/(5-4x)的最小值为4-1/4=15/4