Sửa đề:

\(A=\dfrac{3}{5}+\dfrac{3}{20}+\dfrac{3}{44}+\dfrac{3}{77}\)

\(A=2.\left(\dfrac{3}{5}+\dfrac{3}{20}+\dfrac{3}{44}+\dfrac{3}{77}\right)\)

\(A=\dfrac{6}{10}+\dfrac{6}{40}+\dfrac{6}{88}+\dfrac{6}{154}\)

\(A=6.\left(\dfrac{1}{2.5}+\dfrac{1}{5.8}+\dfrac{1}{8.11}+\dfrac{1}{11.14}\right)\)

\(A=6.\left(\dfrac{1}{2}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{14}\right)\)

\(A=6.\left(\dfrac{1}{2}-\dfrac{1}{14}\right)\)

\(A=6.\dfrac{6}{14}\)

\(A=\dfrac{36}{14}=\dfrac{18}{7}\)

\(=\dfrac{1}{5}.3+\dfrac{1}{5}.\dfrac{3}{4}+\dfrac{1}{11}.\dfrac{3}{4}+\dfrac{1}{11}.\dfrac{3}{7}\)

\(=\dfrac{1}{5}.\left(3+\dfrac{3}{4}\right)+\dfrac{1}{11}.\left(\dfrac{3}{4}+\dfrac{3}{7}\right)\)

\(=\dfrac{1}{5}.\dfrac{15}{4}+\dfrac{1}{11}.\dfrac{33}{28}=\dfrac{3}{4}+\dfrac{3}{28}=\dfrac{6}{7}\)

a)18.17-3.6.37

=18.17-(3.6).37

=18.17-18.37

=18.(17-37)

=18.(-20)

=-360

\(\dfrac{-5}{10}+\dfrac{12}{28}-\dfrac{3}{27}-\dfrac{7}{18}+\dfrac{20}{35}\\ =\left(\dfrac{-1}{2}-\dfrac{1}{9}-\dfrac{7}{18}\right)+\left(\dfrac{3}{7}+\dfrac{4}{7}\right)\\ =\left(\dfrac{-9}{18}-\dfrac{2}{18}-\dfrac{7}{18}\right)+\dfrac{7}{7}\\ =\dfrac{-18}{18}+1\\ =\left(-1\right)+1\\ =0\)

Cả 2 dãy mỗi dãy nhóm 2 số lại

a ) 2 - 3 + 4 - 5 + 6 - 7 + 8 - ... + 209 + 210

( 2 - 3 ) + ( 4 - 5 ) + ( 6 - 7 ) + ( 8 - 9 ) + ... + ( 207 - 208 ) + ( 209 + 210 )

= - 1 + ( -1 ) + ( - 1 ) + ( - 1 ) + ... + ( - 1 ) + 219

Bài này hơi kì kì sao ấy !

Đây là toán lớp 6 mà lại là tính hợp lí, thuộc vào chương số nguyên nên mấy bé lớp 5,4,3,2,1 đừng dại gì mà giải nhé 

a = 1/5-1/8 +1/8-1/11+....+1/602-1/605 = 1/5-(1/8-1/8) -(1/11-1/11)-......-(1/602-1/602)-1/605

1/5-1/605=120/605=24/121 

câu b bạn làm tương tự nhé 

a) (3x - 1)³ + 17 = 710 : 5

(3x - 1)³ + 17 = 142

(3x - 1)³ = 142 - 17

(3x - 1)³ = 125

(3x - 1)³ = 5³

3x - 1 = 5

3x = 5 + 1

3x = 6

x = 6 : 3

x = 2