7 10 = ( )( ) ( )+ + + + 12 6 12 5 9 3 9 3 3 12 5 9 3

2 .3 2 .3 5 .7 5 .7 10

= ( )

( ) ( )

+ + + +

12 6 12 5 9 3 9 3 3 12 5 9 3