c) \(\left(11+12+13+...+19\right).\left(6.8-48\right)=\left(11+12+13+...+19\right).\left(48-48\right)\)

                                                                                         \(=\left(11+12+13+...+19\right).0\)

                                                                                         \(=0\)

Hok "tuốt" nha^^

b) \(\left(500.9-250.18\right).\left(1+2+3+...+9\right)=\left(250.2.9-250.18\right).\left(1+2+...+9\right)\)

                                                                                             \(=\left(250.18-250.18\right).\left(1+2+3+...+9\right)\)

                                                                                             \(=0.\left(1+2+3+...+9\right)\)

                                                                                             \(=0\)

Hok tốt nha^^ (lần 2)

\(5-\dfrac{2}{3}-\dfrac{14}{15}+\dfrac{1}{35}-\dfrac{62}{63}-\dfrac{98}{99}-\dfrac{142}{143}\)

\(=5-\left(1-\dfrac{1}{3}\right)-\left(1-\dfrac{1}{15}\right)+\dfrac{1}{35}-\left(1-\dfrac{1}{63}\right)-\left(1-\dfrac{1}{99}\right)-\left(1-\dfrac{1}{143}\right)\)

\(=5-1+\dfrac{1}{1\cdot3}-1+\dfrac{1}{3\cdot5}+\dfrac{1}{5\cdot7}-1+\dfrac{1}{7\cdot9}-1+\dfrac{1}{9\cdot11}-1+\dfrac{1}{11\cdot13}\)

\(=1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+...+\dfrac{1}{11}-\dfrac{1}{13}\)

\(=1-\dfrac{1}{13}=\dfrac{12}{13}\)

a, ( 532 x 7 - 266 x 14 ) x ( 532 x 7 + 266 ) 

= 3724 - 3714 x 3724 + 266

= 0 x 3990

= 0

b, 117 x ( 36 + 62 ) - 17 x ( 62 + 36 )

= 117 x 98 - 17 x 98 

= 11466 - 1666

= 9800

c, ( 145 x 99 + 145 ) - ( 143 x 101 -143 )

= 14500  - 14300

= 200 

\(a;343-4\times\left(x+1\right)=143\)

\(4\times\left(x+1\right)=343-143\)

\(4\times\left(x+1\right)=200\)

\(x+1=200:4\)

\(x+1=50\)

\(x=50-1=49\)

Mấy câu hỏi trẻ trâu thì tự tính nhé

\(\frac{1}{5.8}+\frac{1}{8.11}+...+\frac{1}{x.\left(x+3\right)}=\frac{101}{1540}\)

\(\Leftrightarrow\frac{1}{3}.\left(\frac{3}{5.8}+\frac{3}{8.11}+...+\frac{3}{x.\left(x+3\right)}\right)=\frac{101}{1540}\)

\(\Leftrightarrow\frac{1}{3}\left(\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{x}-\frac{1}{x+3}\right)=\frac{101}{1540}\)

\(\Leftrightarrow\frac{1}{3}.\left(\frac{1}{5}-\frac{1}{x+3}\right)=\frac{101}{1540}\)

\(\Leftrightarrow\frac{1}{5}-\frac{1}{x+3}=\frac{303}{1540}\)

\(\Leftrightarrow\frac{1}{x+3}=\frac{1}{308}\)

\(\Leftrightarrow x+3=308\)

\(\Leftrightarrow x=305\)

Vậy x=305

\(131+\left(26-3\times x\right):5=135\)

\(\left(26-3\times x\right):5=135-131\)

\(\left(26-3\times x\right):5=4\)

\(26-3\times x=4\times5\)

\(26-3\times x=20\)

\(3\times x=26-20\)

\(3\times x=6\)

\(x=6:3=2\)

(129,3 - 60,8 ) x 5,2 + 143,8  = 500

=145x(99+1)-143x(101-1)

=145x100 - 143x100

=100x(145-143)

=100x2

=200

chịu haizz

cái nào dễ thì làm khó bỏ đi nhé

thì bn hỏi làm j

(145 x 99 + 145) - (143 x 102 - 143)

=(145 x (99+1) - (143 x (102-1)

=(145 x 100) - (143 x 101)

=14500 - 14443

=57

Chúc bạn học tốt .