来自范卫红的问题
(2013•成都模拟)计算:100+121+144+169+…+400=______.
(2013•成都模拟)计算:100+121+144+169+…+400=______.
1回答
2020-02-28 00:57
(2013•成都模拟)计算:100+121+144+169+…+400=______.
(2013•成都模拟)计算:100+121+144+169+…+400=______.
100+121+144+169+…+400,
=102+112+122+…+202,
=(12+22+32+42+…202)-(12+22+32+42+52+62+72+82+92),
=20×(20+1)×(2×20+1)6