.987654321×1235-987654322×1234
=987654321×(1234+1)-(987654321+1)×1234
=987654321×1234+987654321-987654321×1234-1234
=987654321-1234
=987653087.----把这个看明白吧!
2.20052006×20062005-20052005×20062006,
=20052006×(20062006-1)-20052005×20062006,
=20052006×20062006-20052006-20052005×20062006,
=20052006×20062006-20052005×20062006-20052006,
=(20052006-20052005)×20062006-20052006,
=20062006-20052006,
=10000
1+2-3+4+5-6+7+8-9+…+58+59-60,
=(1+2-3)+(4+5-6)+(7+8-9)+…+(58+59-60),
=0+3+6+…+57,
=(0+57)×20÷2,
=570.
--------------------求采纳哦!