21/23 乘以 24 ,怎样算简便 找规律：1/4 4/9 9/16 ( ) ( ) ( )

21/23 乘以 24
=21/23×（23＋1）
=21/23×23＋21/23×1
=21＋21/23
=21又21/23
1/4 4/9 9/16 (16/25 ) (25/36 ) (36/49 )
分子为1,2,3,4,5,6,……的平方
分母为2,3,4,5,6,7,……的平方