20² — 19² +18²—17² +.+2² — 1²=
来源:学生作业帮 编辑:搜搜做题作业网作业帮 分类:数学作业 时间:2024/08/11 21:33:33
20² — 19² +18²—17² +.+2² — 1²=
要简便的,就是简算.
)
要简便的,就是简算.
)
![20² — 19² +18²—17² +.+2² — 1²=](/uploads/image/z/5444471-47-1.jpg?t=20%26%23178%3B+%E2%80%94+19%26%23178%3B+%2B18%26%23178%3B%E2%80%9417%26%23178%3B+%2B.%2B2%26%23178%3B+%E2%80%94+1%26%23178%3B%3D)
因为m²-n²=(m+n)*(m-n)
20²-19²=(20+19)*(20-19)=39
18²-17²=(18+17)*(18-17)=35
16²-15²=(16+15)*(16-15)=31
以此类推
.
2²-1²=(2+1)*(2-1)=3
原式=39+35+31+...+7+3
=(39+3)+(35+7)+(31+11)+(27+15)+(23+19)
=42*5
=210
再问: 谢谢你!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
20²-19²=(20+19)*(20-19)=39
18²-17²=(18+17)*(18-17)=35
16²-15²=(16+15)*(16-15)=31
以此类推
.
2²-1²=(2+1)*(2-1)=3
原式=39+35+31+...+7+3
=(39+3)+(35+7)+(31+11)+(27+15)+(23+19)
=42*5
=210
再问: 谢谢你!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
20² — 19² +18²—17² +.+2² — 1²=
20²-19²+18²-17²+.+2²-1² (过程)
20²-19²+18²-17²+16²-15²+.+2
20²-19²+18²-17²+.4²-3²+2²
20²-19²+18²-17²+16²-15²+2²
计算:1×2²+2×3²+3×4²+...+18×19²+19×20²
50²—49²+48²—47²+46²—……+2²-1
1²+3²+5²+……+(2n-1)²=————
3²—1²=8×1 5²—3²=8×2 7²—5²=8×3
有一组等式:①2²—1²=3 ②3²—2²=5 ③4²—3²
1²+2²+3²+4²+.+19²+20²
(X+Y)²(———)²=X四次方-2X²Y²+Y四次方