无限* 0.GydF4y2Ba

$\ begin {对齐} f（x）= x，\ \ g（x）＆= \ dfrac {2} {x ^ 3} \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \ int \ infty} f（x）g（x）＆= \，？\结束{对齐}GydF4y2Ba$