(9又2/7+7又2/9)/(5/7+5/9) =(65/7+65/9)/(5/7+5/9)=13*(5/7+5/9)/(5/7+5/9)=13
(9 2/7+7 2/9)/(5/7+5/9)=(65/7+65/9)/(5/7+5/9)=13