1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/7
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
A = 1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56
A = 1/1.2 + 1/2.3 + 1/3.4 + 1/4.5 + 1/5.6 + 1/6.7 + 1/7.8
A = 1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6 + 1/6 - 1/7 + 1/7 - 1/8
A = 1 + ( -1/2 + 1/2 ) + ( -1/3 + 1/3 ) + ( -1/4 + 1/4 ) + ( -1/5 + 1/5 ) + ( -1/6 + 1/6 ) + ( -1/7 + 1/7 ) - 1/8
A = 1 + 0 + 0 + 0 + 0 + 0 + 0 - 1/8
A = 1 - 1/8
A = 7/8
* Sửa đề tí nhé
B = 3/2 - 5/6 + 7/12 - 9/20 + 11/30 - 13/42 + 15/56
B = 3/1.2 - 5/2.3 + 7/3.4 - 9/4.5 + 11/5.6 - 13/6.7 + 15/7.8
B = 3 - 3/2 - 5/2 - ( -5/3 ) + 7/3 - 7/4 - 9/4 - ( -9/5 ) + 11/5 - 11/6 - 13/6 - ( -13/7 ) + 15/7 - 15/8
B = 3 - 3/2 - 5/2 + 5/3 + 7/3 - 7/4 - 9/4 + 9/5 + 11/5 - 11/6 - 13/6 + 13/7 + 15/7 - 15/8
B = 3 + ( -3/2 - 5/2 ) + ( 5/3 + 7/3 ) + ( -7/4 - 9/4 ) + ( 9/5 + 11/5 ) + ( -11/6 - 13/6 ) + ( 13/7 + 15/7 ) - 15/8
B = 3 + -4 + 4 + -4 + 4 + -4 + 4 - 15/8
B = 3 + 0 + 0 + 0 - 15/8
B = 3 - 15/8
B = 9/8
![](https://rs.olm.vn/images/avt/0.png?1311)
em lớp 6 nha
B= 1/2 + 1/6 + 1/12 +1/20 + 1/30 + 1/42 + 1/56 + 1/72
B= 1/1*2 + 1/2*3 + 1/3*4 + 1/4*5 + 1/5*6 + 1/6*7 + 1/7*8 + 1/8*9
B=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9
B=1+0-0-0-0-0-0-0-1/9
B=1-1/9
B=8/9
k em nha
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(\dfrac{3}{8}+\dfrac{7}{12}+\dfrac{10}{16}+\dfrac{10}{24}\)
\(=\dfrac{3}{8}+\dfrac{7}{12}+\dfrac{5}{8}+\dfrac{5}{12}\)
\(=\left(\dfrac{3}{8}+\dfrac{5}{8}\right)+\left(\dfrac{7}{12}+\dfrac{5}{12}\right)\)
\(=1+1\)
\(=2\)
b) \(\dfrac{4}{6}+\dfrac{7}{13}+\dfrac{17}{9}+\dfrac{19}{13}+\dfrac{1}{9}+\dfrac{14}{6}\)
\(=\dfrac{2}{3}+\dfrac{7}{13}+\dfrac{17}{9}+\dfrac{19}{13}+\dfrac{1}{9}+\dfrac{7}{3}\)
\(=\left(\dfrac{2}{3}+\dfrac{7}{3}\right)+\left(\dfrac{7}{13}+\dfrac{19}{13}\right)+\left(\dfrac{17}{9}+\dfrac{1}{9}\right)\)
\(=3+2+2\)
\(=7\)
c) \(\dfrac{1}{2}+\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}\)
\(=\dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+\dfrac{1}{4\cdot5}+\dfrac{1}{5\cdot6}+\dfrac{1}{6\cdot7}\)
\(=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}\)
\(=1-\dfrac{1}{7}\)
\(=\dfrac{6}{7}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56
= 1/1x2 + 1/2x3 + 1/3x4 + 1/4x5 + 1/5x6 + 1/6x7 + 1/7x8
= 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6 + 1/6 - 1/7 + 1/7 - 1/8
= 1 - 1/8
= 7/8
1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56
= 1/1x2 + 1/2x3 + 1/3x4 + 1/4x5 + 1/5x6 + 1/6x7 + 1/7x8
= 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/7 - 1/8
= 1 - 1/8
= 7/8
![](https://rs.olm.vn/images/avt/0.png?1311)
A=1/2.3+1/3.4+1/4.5+1/5.6+1/6.7+1/7.8+1/8.9+1/9.10+1/10.11
A=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11
A=1/2-(1/3-1/3)-(1/4-1/4)-(1/5-1/5)-(1/6-1/6)-(1/7-1/7)-(1/8-1/8)-(1/9-1/9)-(1/10-1/10)-1/11
A=1/2-1/11 A=11/22-2/22
A=9/22
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{1}{2}\)+\(\frac{1}{6}\)+ \(\frac{1}{12}\)+\(\frac{1}{20}\)+\(\frac{1}{30}\)+\(\frac{1}{42}\)+\(\frac{1}{56}\)=\(\frac{7}{8}\)
1/2+1/6+1/12+1/20+1/30+1/42+1/56=7/8=0.875
kick mik nha xin đó
![](https://rs.olm.vn/images/avt/0.png?1311)
\(1\frac{1}{2}+2\frac{1}{6}+3\frac{1}{12}+4\frac{2}{20}+5\frac{1}{30}+6\frac{1}{42}+7\frac{1}{56}+8\frac{1}{72}+9\frac{1}{90}+\frac{1}{10}\)\(=\frac{3}{2}+\frac{13}{6}+\frac{37}{12}+\frac{81}{20}+\frac{151}{30}+\frac{253}{42}+\frac{393}{56}+\frac{577}{72}+\frac{811}{90}+\frac{1}{10}=46\)
k nha
๖ۣۜH๖ۣۜU๖ۣۜY ๖ۣۜR๖ۣۜI๖ۣۜO
Đầu tiên , cộng các phần nguyên lại với nhau , ta có :
( 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 ) + ( 12 +16 +112 +120 +130 +142 +156 +172 +190 +110 )
= 45 + (16 +130 )+12 +112 +120 +142 +156 +172 +190 +110
sau khi cộng trong ngoặc , ta được 6 / 30 , rút gọn tối giản còn 1 / 5
= 45 + (15 +120 )+12 +112 +142 +156 +172 +190 +110
sau khi cộng trong ngoặc và rút gọn tối giản , ta được 1 / 4
= 45 + (14 +12 )+112 +142 +156 +172 +190 +110
sau khi cộng trong ngoặc rồi rút gọn , ta được 3 / 4
= 45 + (34 +112 )+142 +156 +172 +190 +110
rút gọn lại ta được 5 / 6
= 45 + (56 +142 )+156 +172 +190 +110
rút gọn tối giản ra 6 / 7
= 45 + (67 +156 )+172 +190 +110
sau khi tính trong ngoặc rút gọn được 7 / 8
= 45 + (78 +172 )+190 +110
tính trong ngoặc rồi rút gọn ra 8 / 9
= 45 + (89 +190 )+110
cũng rút gọn tiếp ta được 9 / 10
= 45 + (910 +110 )
= 45 + 1
= 46
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+......+\frac{1}{56}\)
\(=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+......+\frac{1}{7.8}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+.....+\frac{1}{7}-\frac{1}{8}\)
\(=1-\frac{1}{8}\)
\(=\frac{7}{8}\)
`1/2+1/6+1/12+1/20+1/30+1/42 +1/56`
`=1/(1xx2)+1/(2xx3)+1/(3xx4)+1/(4xx5)+1/(5xx6) + 1/(6xx7) +1/(7xx8)`
`=1-1/2+1/2-1/3+......+1/7-1/8`
`=1-1/8`
`=7/8`
1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56
= 1/1x2 + 1/2x3 + 1/3x4 + 1/4x5 + 1/5x6 + 1/6x7 + 1/7x8
= 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6 + 1/6 - 1/7 + 1/7 - 1/8
= 1 - 1/8
= 7/8