9.9×9.9+0.99 简便计算
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9.9×9.9+0.99 简便计算
9.9×9.9+0.99 简便计算
9.9×9.9+0.99 简便计算
9.9×9.9+0.99 =9.9×9.9+9.9×0.1 =9.9×(9.9+0.1) =9.9×10 =99
9.9*(10-0.1)+0.99--->9.9*10-0.99+0.99=99
9.9*9.9+9.9*0.1=99
(10-0.1)*9.9+0.99=10*9.9-0.99+0.99=99
收起
9.9x(9.9+0.1)=9.9x10=99
设0.99为a 原试=10a x 10a + a