BẠN NÀO BIẾT THÌ GIÚP MÌNH VỚI !!!!!!!

1) \(1+\frac{1}{3}+1\frac{91}{27}+\frac{1}{81}\)

\(=1+\frac{1}{3}+4+\frac{10}{27}+\frac{1}{81}\)

\(=\left(1+4\right)+\left(\frac{1}{3}+\frac{10}{27}+\frac{1}{81}\right)\)

\(=5+\frac{58}{81}=5\frac{58}{81}\)

2) \(\frac{1}{78}+\frac{1}{91}+\frac{1}{105}+\frac{1}{120}+\frac{1}{136}\)

\(=\frac{1}{6\times13}+\frac{1}{13\times7}+\frac{1}{7\times15}+\frac{1}{15\times8}+\frac{1}{8\times17}\)

\(=\frac{1}{6}-\frac{1}{13}+\frac{1}{13}-\frac{1}{7}+\frac{1}{7}-\frac{1}{15}+\frac{1}{15}-\frac{1}{8}+\frac{1}{8}-\frac{1}{17}\)

(gạch bỏ các số giống nhau)

\(=\frac{1}{6}-\frac{1}{17}=\frac{11}{102}\)

3)  \(\frac{1}{6}+\frac{1}{30}+\frac{1}{70}+\frac{1}{126}\)

\(=\frac{1}{2\times3}+\frac{1}{3\times10}+\frac{1}{10\times7}+\frac{1}{7\times18}\)

\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{10}+\frac{1}{10}-\frac{1}{7}+\frac{1}{7}-\frac{1}{18}\)

\(=\frac{1}{2}-\frac{1}{18}=\frac{4}{9}\)

chúc bn học tốt!!

công chúa ôri ơi mk viết nhầm đề bài 1 

đề bài là 1+1/3+1/9+1/27+1/81

bạn trả lời giúp mk với mk cần gấp lắm

cảm ơn

a)\(1+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}\)

\(=1+\frac{1}{1\times3}+\frac{1}{3\times3}+\frac{1}{3\times9}+\frac{1}{9\times9}\)

\(=1+1-\frac{1}{3}+\frac{1}{3}-\frac{1}{3}+\frac{1}{3}-\frac{1}{9}+\frac{1}{9}-\frac{1}{9}\)

\(=2-\frac{1}{9}=1\frac{8}{9}\)

BN VIẾT NHẦM CÂU 1 , THẢO NÀO MK THẤY RA SỐ TO QUÁ!

\(\frac{1}{3}+\frac{1}{6}+\frac{1}{12}+\frac{1}{48}+\frac{1}{96}+\frac{1}{192}\)

= \(\left(\frac{1}{3}+\frac{1}{6}\right)+\left(\frac{1}{12}+\frac{1}{24}\right)+\left(\frac{1}{48}+\frac{1}{96}\right)+\frac{1}{192}\)

=               \(\left(\frac{1}{2}+\frac{1}{8}\right)+\left(\frac{1}{32}+\frac{1}{192}\right)\)

=                              \(\frac{5}{8}+\frac{1}{192}\)

=                                    \(\frac{121}{192}\)

ko ai bết đâu

94.2023+2023:1/6

 =94.2023+2023.6

 =(94+6).2023

 =100.2023

 =202300

\(\left(1-\frac{1}{2}\right)\left(1-\frac{1}{3}\right)\left(1-\frac{1}{4}\right)......\left(1-\frac{1}{204}\right)\)

\(=\frac{1}{2}.\frac{2}{3}.\frac{3}{4}.....\frac{203}{204}\)

\(=\frac{1}{204}\)

\(\text{Sửa đề }\left(1-\frac{1}{2}\right)\times\left(1-\frac{1}{3}\right)\times\left(1-\frac{1}{4}\right)\times....\times\left(1-\frac{1}{203}\right)\times\left(1-\frac{1}{204}\right)\)

\(=\frac{1}{2}\times\frac{2}{3}\times\frac{3}{4}\times....\times\frac{202}{203}\times\frac{203}{204}\)

\(=\frac{1\times2\times3\times...\times202\times203}{2\times3\times4\times...\times203\times204}\)

\(=\frac{1}{204}\)

\(\left(1-\frac{1}{2}\right)\)\(.\left(1-\frac{1}{3}\right)\)\(...\left(1-\frac{1}{203}\right).\left(1-\frac{1}{204}\right)\)

\(=\frac{1}{2}.\frac{2}{3}....\frac{202}{203}.\frac{203}{204}\)

=\(\frac{1.2....202.203}{2.3....203.204}\)

=\(\frac{1}{204}\)

Lạy ông đi qua,bà đi lại.

Cho con một tích đúng

đề bài, tui ko còn giữ sách lớp 6 đâu
 

cho n là số tự nhiên

a,   (n+ 10) (n+ 15) chia hết cho 2

b,    n (n+ 1) (n+2) chia hết cho 2 và 3

c,     n (n+ 1) (2n+1) chia hết cho 2 và 3

A=1.4+1/4.7+1/7.10+...+1/91.94

=1/3.(3/1.4+3/4.7+3/7.10+...+3/91.94)

=1/3.(1-1/4+1/4-1/7+1/7-1/10+...+1/91-1/94)

=1/3.(1-1-94)

=1/3.(93/94)

=31/94

\(\frac{1}{1\cdot4}+\frac{1}{4\cdot7}+\frac{1}{7\cdot10}+...+\frac{1}{91\cdot94}\)

\(=\frac{1}{3}\left(\frac{3}{1\cdot4}+\frac{3}{4\cdot7}+\frac{3}{7\cdot10}+...+\frac{3}{91\cdot94}\right)\)

\(=\frac{1}{3}\left(1-\frac{1}{94}\right)\)

\(=\frac{1}{3}\cdot\frac{93}{94}\)

\(=\frac{31}{94}\)

\(A=\frac{1}{1\cdot4}+\frac{1}{4\cdot7}+.......+\frac{1}{91\cdot94}\)

\(3A=\frac{3}{1\cdot4}+\frac{3}{4\cdot7}+......+\frac{3}{91\cdot94}\)

\(3A=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+.......+\frac{1}{91}-\frac{1}{94}\)

\(3A=1-\frac{1}{94}=\frac{93}{94}\)

\(A=\frac{93}{94}:3\)