Question

1*2*3*4*5*6*7*8*9的简便计算方法是什么?

Answer 1

1 X 2 X 3 X 4 X 5 X 6 X 7 X 8 X 9

= ( 2 X 3 X 4 X 5 ) X ( 6 X 7 X 8 X 9 )

= ( 10 X 12 ) X ( 54 X 56 )

= 120 X ( 55 - 1 )( 55 + 1 )

= 120 X ( 55" - 1" )

= 30 X 4 X ( 3025 - 1 )

= 30 X ( 12100 - 4 )

= 363000 - 120

= 362880