證明恆等式

5+y/9 - 2y+3/3 = - 5y+4/9
其實係(5+y)/9 - (2y+3)/3 = - (5y+4)/9
左式=(5+y)/9 - (2y+3)/3
=(5+y)/9 - (6y+9)/9
=(5+y-6y-9)/9
=(-5y-4)/9
=-(5y+4)/9
=右式

2007-12-14 23:59:33 補充：
參考資料:我每次都攞第一