từ 1 đến 20 có 20 số hạng nên 20*(20+1)/2=210
Vay 1+2+3+4+5+6+7+...+20=210
Đúng 0
Bình luận (0)
Các câu hỏi tương tự
7/2.x-3/4=5/6– -2/3
5/6-(20%.x-3/4)=x+1/2
1+2+3+4+5+6+7+8+9+...+20
, , ?
3 + 4 … 6
6 + 1 … 6
5 + 1 … 6
3 + 4 … 7
5 + 2 … 6
7 – 5 … 3
7 – 4 … 4
7 – 2 … 5
7 – 6 … 1
Đọc tiếp
>, <, = ?
| 3 + 4 … 6 | 6 + 1 … 6 | 5 + 1 … 6 |
| 3 + 4 … 7 | 5 + 2 … 6 | 7 – 5 … 3 |
| 7 – 4 … 4 | 7 – 2 … 5 | 7 – 6 … 1 |
19 tháng 8 2019 lúc 11:16
e,Afrac{1}{2}+frac{5}{6}+frac{11}{12}+frac{19}{20}+frac{29}{30}+frac{41}{42}left(1-frac{1}{2}right)+left(1-frac{1}{6}right)+left(1-frac{1}{12}right)+left(1-frac{1}{20}right)+left(1-frac{1}{20}right)+left(1-frac{1}{42}right)Rightarrow A1-frac{1}{2}+1-frac{1}{6}+1-frac{1}{12}+1-frac{1}{20}+1-frac{1}{30}+1-frac{1}{42}4-left(frac{1}{2}+frac{1}{6}+frac{1}{12}+frac{1}{20}+frac{1}{30}+frac{1}{42}right)Rightarrow A4-left(frac{1}{1.2}+frac{1}{2.3}+frac{1}{3.4}+frac{1}{4.5}+frac{1}{5.6}+frac{1}{6.7}right)...
Đọc tiếp
e,\(A=\frac{1}{2}+\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+\frac{29}{30}+\frac{41}{42}=\left(1-\frac{1}{2}\right)+\left(1-\frac{1}{6}\right)+\left(1-\frac{1}{12}\right)+\left(1-\frac{1}{20}\right)+\left(1-\frac{1}{20}\right)+\left(1-\frac{1}{42}\right)\)
\(\Rightarrow A=1-\frac{1}{2}+1-\frac{1}{6}+1-\frac{1}{12}+1-\frac{1}{20}+1-\frac{1}{30}+1-\frac{1}{42}=4-\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}\right)\)
\(\Rightarrow A=4-\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}\right)=4-\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\right)\)
\(\Rightarrow A=4-\left(\frac{1}{1}-\frac{1}{7}\right)=4-\frac{6}{7}=3\frac{1}{7}\)
Tính:
6 + 1 = 5 + 2 = 4 + 3 =
1 +6 = 2 + 5 = 3 + 4 =
7 - 6 = 7 -5 = 7 - 4 =
7 - 1 = 7 -2 = 7 - 3 =
Tính:
4 + 3 …
5 + 2 …
6 + 1 …
3 + 4 …
2 + 5 …
1 + 6 …
7 – 4 …
7 – 5 …
7 – 6 …
7 – 3 …
7 – 2 …
7 – 1 …
Đọc tiếp
Tính:
| 4 + 3 = … | 5 + 2 = … | 6 + 1 = … |
| 3 + 4 = … | 2 + 5 = … | 1 + 6 = … |
| 7 – 4 = … | 7 – 5 = … | 7 – 6 = … |
| 7 – 3 = … | 7 – 2 = … | 7 – 1 = … |
Bài 3: Tính1 + 5 2 + 3 3 + 6 4 + 5 5 + 1 6 + 2 7 + 1 8 + 1 9 + 0 10 + 211 + 2 1 + 3 2 + 6 3 + 7 4 + 2 5 + 2 6 + 3 7 + 3 8 + 2 9 + 1 10 + 0 11 + 3 1 + 4 2 + 8 3 + 2 4 + 1 5 + 4 6 + 4 7 + 2 8 + 0 9 + 2 10 + 6 11 + 6 Bài 4: Tính6 - 2 3 - 1 4 - 2 5 - 2 8 - 5 10 - 6 4 - 3 3 - 3 5 - 1 2 - 2 3 - 1 4 - 1 2 - 1 4 - 3 5 - 0 9 - 4 8 - 6 7 - 3 8 - 4 7 - 6 9 - 5 7 - 75 - 3 5 - 36 - 3 7 - 3 7 - 6 6 - 5 9 - 7 9 - 3 8 - 8 8 - 0 5 - 3 Bài 5: Tính6 - 2 5 + 2 9 - 5 2 + 0 8 + 2 4 - 4 7 - 3 3 + 6 7 + 2 9 - 5 3 + 6 1...
Đọc tiếp
Bài 3: Tính
1 + 5 =
2 + 3 =
3 + 6 =
4 + 5 =
5 + 1 =
6 + 2 =
7 + 1 =
8 + 1 =
9 + 0 =
10 + 2=
11 + 2 =
1 + 3 =
2 + 6 =
3 + 7 =
4 + 2 =
5 + 2 =
6 + 3 =
7 + 3 =
8 + 2 =
9 + 1 =
10 + 0 =
11 + 3 =
1 + 4 =
2 + 8 =
3 + 2 =
4 + 1 =
5 + 4 =
6 + 4 =
7 + 2 =
8 + 0 =
9 + 2 =
10 + 6 =
11 + 6 =
Bài 4: Tính
6 - 2 =
3 - 1 =
4 - 2 =
5 - 2 =
8 - 5 =
10 - 6 =
4 - 3 =
3 - 3 =
5 - 1 =
2 - 2 =
3 - 1 =
4 - 1 =
2 - 1 =
4 - 3 =
5 - 0 =
9 - 4 =
8 - 6 =
7 - 3 =
8 - 4 =
7 - 6 =
9 - 5 =
7 - 7=
5 - 3 =
5 - 3=
6 - 3 =
7 - 3 =
7 - 6 =
6 - 5 =
9 - 7 =
9 - 3 =
8 - 8 =
8 - 0 =
5 - 3 =
Bài 5: Tính
6 - 2 =
5 + 2 =
9 - 5 =
2 + 0 =
8 + 2 =
4 - 4 =
7 - 3 =
3 + 6 =
7 + 2 =
9 - 5 =
3 + 6 =
1 + 5 =
7 - 6 =
7 + 1 =
3 + 5 =
2 - 1 =
6 + 3 =
5 + 2 =
9 - 4 =
6 + 4 =
4 + 2 =
6 + 1=
7 - 7=
4 + 3 =
7 + 3 =
5 - 2 =
6 - 5 =
8 - 6 =
6 - 4 =
7 - 3 =
10 + 0 =
5 +4 =
8 - 2 =
1=10 2=20 3=3= 4=40 5=50 6=60 7=70 8=80 9=90 10=?