函數(shù)f(x)=ax+b/x,(a>0,b>0)叫做雙鉤函數(shù).
該函數(shù)是奇函數(shù),圖象關(guān)于原點(diǎn)對(duì)稱.位于第一、三象限.
當(dāng)x>0時(shí),由基本不等式可得：y ≥2√ab
當(dāng)且僅當(dāng)ax=b/x,即x=√(b/a)時(shí)取等號(hào).
故其頂點(diǎn)坐標(biāo)為(√(b/a),2√ab),圖象在(0,√(b/a))上是單調(diào)遞減的,在(√(b/a),+∝)上是單調(diào)遞增
同理：當(dāng)x