简便算法(用乘法的公式计算)(1) 198*198(2) 102*102(3) 29*29+21*21+42*29
3个回答

(1) 198*198

=(200-2)*(200-2)

=(200-2)^

=200^-2*200*2+2^

=40000-800+4

=39204

(2) 102*102

=(100+2)*(100+2)

=(100+2)^

=100^+2*100*2+2^

=10000+400+4

=10404

(3) 29*29+21*21+42*29

=29*29+21*21+(21+21)*29

=29*29+21*21+21*29+21*29

=29*(29+21)+21*(21+29)

=29*50+21*50

=(29+21)*50

=50*50

=2500

^表示平方