/x1/alnx/xe/loga1ln/x/sics/oxin/ta2sec/xx/sectan/xscox/arcin21/rosx21x/arctnx21/o/uv/v/2kdx1dxln21arctx2dsincosxiinds2secxtaoxsectanxdsecxoxexxadlnxtcoscoxdlixsensectacxlox21darcta2xln21dxa2lxa2rcsin等价无穷小 0xsintarcixtnl(1)xecos21xaln渐近线 klimxfblixf曲率 k/3/21y