Question

a) A = \(\frac{4}{3\cdot7}+\frac{4}{7\cdot11}+\frac{4}{11\cdot5}+...+\frac{4}{107\cdot111}\)

b) B = \(\frac{6}{15\cdot18}+\frac{6}{18\cdot21}+\frac{6}{21\cdot24}+...+\frac{6}{87\cdot90}\)

c) C = \(\frac{1}{1\cdot6}+\frac{1}{6\cdot11}+\frac{1}{11\cdot16}+...+\frac{1}{51\cdot56}\)

d) D = \(\frac{1}{1\cdot2\cdot3}+\frac{1}{2\cdot3\cdot4}+\frac{1}{3\cdot4\cdot5}+...+\frac{1}{98\cdot99\cdot100}\)

Answer 1

a) A = 1/3 - 1/7 + 1/7 - 1/11 +......+1/107 - 1/111

A = 1/3 - 1/111

A = ..............Bạn tự tính nhé!

b) B = 2.(3/15.18 + 3/18.21 +........+3/87.90)

B = 2.(1/15 - 1/18 + 1/18 - 1/21 +........+1/87 - 1/90)

B = 2.(1/15 - 1/90)

B = 2.5/90

B =......Tự tính nhé!

C ; D làm tương tự nhé!

Answer 2

yêu cầu là gì vậy

Answer 3

a)

A=\(\frac{4}{3.7}+\frac{4}{7.11}+....+\frac{4}{107.111}=\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-.....+\frac{1}{107}-\frac{1}{111}=\frac{1}{3}-\frac{1}{111}=\frac{108}{333}\)

Answer 4

b)B=\(\frac{6}{15.18}+\frac{6}{18.21}+...+\frac{6}{87.90}=6\left(\frac{1}{15.18}+\frac{1}{18.21}+...+\frac{1}{87.90}\right)\)

\(=6\left(\frac{3}{15.18}+\frac{3}{18.21}+...+\frac{3}{87.90}\right)=6\left(\frac{1}{15}-\frac{1}{18}+\frac{1}{18}-...-\frac{1}{90}\right)\)

\(=6\left(\frac{1}{15}-\frac{1}{90}\right)=6.\frac{1}{18}=\frac{1}{3}\)

Answer 5

a)\(A=\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{1}{107}-\frac{1}{111}\)

\(A=\frac{1}{3}-\frac{1}{111}\)

\(A=\frac{108}{333}\)

b)\(B=\frac{1}{15}-\frac{1}{18}+\frac{1}{18}-\frac{1}{21}+...+\frac{1}{87}-\frac{1}{90}\)

\(B=\frac{1}{15}-\frac{1}{90}\)

\(B=\frac{1}{18}\)

C,D tương tự

Answer 6

a) A = \(\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{1}{107}-\frac{1}{111}\)

A = \(\frac{1}{3}-\frac{1}{111}\)

A = \(\frac{36}{111}=\frac{12}{37}\)

các câu dưới tương tự

Answer 7

c)

C=\(\frac{1}{1.6}+\frac{1}{6.11}+...+\frac{1}{51.56}=\frac{5}{1.6}+\frac{5}{6.11}+...+\frac{6}{51.56}\)

\(=1-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+...+\frac{1}{51}-\frac{1}{56}=1-\frac{1}{56}=\frac{55}{56}\)

Answer 8

Nguyễn Huy THắng làm câu B sai rùi!

Answer 9

a,A=\(\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+..........+\frac{1}{107}-\frac{1}{111}\)

=\(\frac{1}{3}-\frac{1}{111}\)

=\(\frac{12}{37}\)

b,\(=2.\left(\frac{3}{15.18}+\frac{3}{18.21}+...........+\frac{3}{87.90}\right)\)

=\(2.\left(\frac{1}{15}-\frac{1}{18}+\frac{1}{18}-\frac{1}{21}+...........+\frac{1}{87}-\frac{1}{90}\right)\)

=\(2.\left(\frac{1}{15}-\frac{1}{90}\right)\)

=\(2.\frac{1}{18}\)

=\(\frac{1}{9}\)

c và d tương tự

Answer 10

a) \(A=\frac{4}{3}-\frac{4}{7}+\frac{4}{7}-\frac{4}{11}+...+\frac{4}{107}-\frac{4}{111}\)

\(A=\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{1}{107}-\frac{1}{111}\)

\(A=\frac{1}{3}-\frac{1}{111}\)

\(A=\frac{37}{111}+\left(\frac{-1}{111}\right)\)

\(A=\frac{36}{111}\)

mấy câu sau lười nên ko làm

Answer 11

thanks mấy bạn nha

Answer 12

A=1/3-1/7+1/7-1/9+....+1/107-1/111=1/3-1/111=108/333=12/37