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.