问题 解答题

利用平方差公式计算:

(1)27×33;

(2)5.9×6.1;

(3)99×101;

(4)1005×995.

答案

(1)27×33,

=(30-3)(30+3),

=302-32

=891;

(2)5.9×6.1,

=(6-0.1)(6+0.1),

=62-(0.1)2

=35.99;

(3)99×101,

=(100-1)(100+1),

=1002-12

=9999;

(4)1005×995,

=(1000+5),

=10002-52

=999975.

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