用简便计算法计算 (1)9.9×10.1 (2)899×901 用平方差的公式!
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用简便计算法计算 (1)9.9×10.1 (2)899×901 用平方差的公式!
用简便计算法计算 (1)9.9×10.1 (2)899×901 用平方差的公式!
用简便计算法计算 (1)9.9×10.1 (2)899×901 用平方差的公式!
(10-0.1)(10+0.1) (900-1)(900+1)
(1)9.9×10.1
=(10-0.1)×(10+0.1)
=10^2-0.1^2
=100-0.01
=99.99
(2)899×901
= (900-1)(900+1)
=900^2-1^2
=810000-1
=809999