1000+999-998-997+996+995-994-993+…+104+103-102-101.
1000+999-998-997+996+995-994-993+…+104+103-102-101,
=(1000+999-998-997)+…+(104+103-102-101),
=4+…+4,
=4×225,
=900.
1000+999-998-997+996+995-994-993+…+104+103-102-101.
1000+999-998-997+996+995-994-993+…+104+103-102-101,
=(1000+999-998-997)+…+(104+103-102-101),
=4+…+4,
=4×225,
=900.