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)
B=5/18*21+5/21*24+5/24*27+...+5/123*126
3/5B=3/5(5/18*21+5/21*24+...+5/123*126)
3/5B=3/5*5/18*21+3/5*5/21*24+...+3/5*5/123*126
3/5B=3/18*21+3/21*24+...+3/123*126
3/5B=1/18-1/21+1/21-1/24+...+1/123-1/126
3/5B=1/18-1/126
3/5B=126/2268-18/2268
3/5B=108/2268
3/5B=21
B=21÷3/5
B=21*5/3
B=35
![](https://rs.olm.vn/images/avt/0.png?1311)
\(=\)\(\frac{-3}{5}\)\(+\frac{28.43}{5.28.2}\)\(+\frac{4.7.5}{5.4.6}\)\(+\frac{28.21}{5.21.3}\)
\(=\)\(\frac{-3}{5}\)\(+\frac{43}{10}+\frac{7}{6}+\frac{28}{15}\)
\(=\)\(\frac{-48}{90}+\frac{387}{90}+\frac{85}{90}+\frac{168}{90}\)
\(=\)\(\frac{592}{90}\)
\(=\)\(\frac{296}{45}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
đặt bt trên là A
\(\frac{1}{2}\)A=\(\frac{3}{15.18}+\frac{3}{18.21}+\frac{3}{21.24}+...+\frac{3}{87.90}\)
\(\frac{1}{2}\)A=\(\frac{1}{15}-\frac{1}{18}+\frac{1}{18}-\frac{1}{21}+\frac{1}{21}-....+\frac{1}{87}-\frac{1}{90}\)
\(\frac{1}{2}A=\frac{1}{15}-\frac{1}{90}\)
..... tự tính nhé
![](https://rs.olm.vn/images/avt/0.png?1311)
Câu 1 : \(1,321338308x10^{-4}\)
Câu 2 : \(1316,572106\)
Câu 3 : \(1,641302619x10^{-13}\)
Ủng hộ nhé,tớ đang âm.
![](https://rs.olm.vn/images/avt/0.png?1311)
A= 1/18 nhé bạn
xin lỗi vì mình không viết cách làm..........
![](https://rs.olm.vn/images/avt/0.png?1311)
=\(\frac{1}{2}\cdot\left(\frac{6}{9\cdot15}+\frac{6}{15\cdot21}+\frac{6}{21\cdot27}+...+\frac{6}{99\cdot105}\right)\)
=\(\frac{1}{2}\cdot\left(\frac{1}{9}-\frac{1}{15}+\frac{1}{15}-\frac{1}{21}+\frac{1}{21}-\frac{1}{27}+...+\frac{1}{99}-\frac{1}{105}\right)\)
=\(\frac{1}{2}\cdot\left(\frac{1}{9}-\frac{1}{105}\right)\)
=\(\frac{1}{2}\cdot\left(\frac{35}{315}-\frac{3}{315}\right)\)
=\(\frac{1}{2}\cdot\left(\frac{32}{315}\right)\)
=\(\frac{1\cdot16}{1\cdot315}\)
=\(\frac{16}{315}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Đây là những bài lớp 5+ vậy nên không làm theo kiểu lớp 5 được, cố gắng tìm bài đúng lớp nhé bạn (VNNLL cc)
\(B=\frac{5}{18\cdot21}+\frac{5}{21\cdot24}+\frac{5}{24\cdot27}+...+\frac{5}{123\cdot126}\\ B=\frac{5}{3}\cdot\left(\frac{3}{18\cdot21}+\frac{3}{21\cdot24}+\frac{3}{24\cdot27}+...+\frac{3}{123\cdot126}\right)\\ B=\frac{5}{3}\cdot\left(\frac{1}{18}-\frac{1}{21}+\frac{1}{21}-\frac{1}{24}+\frac{1}{24}-\frac{1}{27}+...+\frac{1}{123}-\frac{1}{126}\right)\\ B=\frac{5}{3}\cdot\left(\frac{1}{18}-\frac{1}{126}\right)\\ B=\frac{5}{3}\cdot\left(\frac{7}{126}-\frac{1}{126}\right)\\ B=\frac{5}{3}\cdot\frac{1}{21}\\ B=\frac{5}{63}\)