x^2-2x<8(x-4)(x+2)<0-2<x<4所以x+2>0y=(x^2-x-5)/(x+2) =(x^2+4x+4-5x-10+1)/(x+2) =[(x+2)^2-5(x+2)+1]/(x+2) =(x+2)+1/(x+2)-5 >=2√(x+2)*[1/(x+2)-5 (当且仅当x+2=1/(x+2)时取到等号） =2-5 =-3所以ymin= 展开
x^2-2x<8(x-4)(x+2)<0-2<x<4所以x+2>0y=(x^2-x-5)/(x+2) =(x^2+4x+4-5x-10+1)/(x+2) =[(x+2)^2-5(x+2)+1]/(x+2) =(x+2)+1/(x+2)-5 >=2√(x+2)*[1/(x+2)-5 (当且仅当x+2=1/(x+2)时取到等号） =2-5 =-3所以ymin=-3 收起
