Question

55*45+66*54+77*63+88*72 用简便方法做

Answer 1

55*45+66*54+77*63+88*72

=(50+5)(50-5) + (60+6)(60-6) + (70+7)(70-7) + (80+8)(80-8)

=50^2 - 5^2 + 60^2 -6^2 +70^2 -7^2 +80^2 -8^2

= (5^2+6^2+7^2+8^2)*(100-1)

= 17400-174

= 17226