y=(x+3)/(x²+5x+10)
=(x+3)/[(x+3)²-(x+3)+4]
當(dāng)x+3=0時(shí) x=-3
當(dāng)x≠-3時(shí),
分子分母同時(shí)除以x+3得
=1/[(x+3)-1+4/(x+3)]
因?yàn)?br/>(x+3)+4/(x+3)≥2√[(x+3)×4/(x+3)]=4
或
(x+3)+4/(x+3)≤-2√[(x+3)×4/(x+3)]=-4
所以,值域?yàn)?[-1/5,1/3]“或”是因?yàn)閷?duì)勾函數(shù)進(jìn)行的分類討論嗎對(duì)啊基本不等式x+4/x≥4或x+4/x≤-4