[ 1/ 25 x 26 + 1/26x27+....+ 1/29x30] x 150 + 103; 1,03 x ( x -1 ) =22

[ 1/25x26 + 1/26x27 + 1/27x28 + 1/28x29 + 1/29x30] x 150 + 103;1,03 x (x-1)=22

[ 1/650 + 1/702 + 1/756 + 1/812 + 1/870] x 150 + 103 ; 1,03 x (x-1) =22

(1/24x25 + 1/25x26 + ... + 1/29x30) x 120 + y : 1/3 = -4

(1/24 - 1/25 + 1/25 - 1/26 + ... + 1/29 - 1/30) x 120 + y x 3 = -4

(1/24 - 1/30) x 120 + y x 3 = -4

1/120 x 120 + y x 3 = -4

=> 1 + y x 3 = -4

=> y x 3 = -4 - 1

=> y x 3 = -5

=> y = -5/3

Vậy x = -5/3

Ủng hộ mk nha ^_-

(1/24x25 + 1/25x26 + ... + 1/29x30) x 120 + y : 1/3 = -4

(1/24 - 1/25 + 1/25 - 1/26 + ... + 1/29 - 1/30) x 120 + y x 3 = -4

(1/24 - 1/30) x 120 + y x 3 = -4

1/120 x 120 + y x 3 = -4

=> 1 + y x 3 = -4

=> y x 3 = -4 - 1

=> y x 3 = -5

=> y = -5/3

Vậy x = -5/3

T_I_C_K mk nha

\(\frac{5}{3\times4}+\frac{5}{4\times5}+\frac{5}{5\times6}+...+\frac{5}{25\times26}+\frac{5}{26\times27}\)

\(=\frac{4-3}{3\times4}+\frac{5-4}{4\times5}+\frac{6-5}{5\times6}+...+\frac{26-25}{25\times26}+\frac{27-26}{26\times27}\)

\(=5\times\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+....+\frac{1}{25}-\frac{1}{26}+\frac{1}{26}-\frac{1}{27}\right)\)

\(=5\times\left(\frac{1}{3}-\frac{1}{27}\right)\)

\(=5\times\frac{8}{27}=\frac{40}{27}\)

\(\frac{5}{3.4}+\frac{5}{4.5}+\frac{5}{5.6}+...+\frac{5}{25.26}+\frac{5}{26.27}\)

\(=5\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{25}-\frac{1}{26}+\frac{2}{26}-\frac{1}{27}\right)\)

\(=5\left(\frac{1}{3}-\frac{1}{27}\right)\)

\(=\frac{40}{27}\)

Thank you!

Đặt A = 1x2+2x3+3x4+...+25x26+26x27

3A = 1 x 2 x 3 - 1 x 2 x 3 + 2 x 3 x 4  -2 x 3 x 4 + ..... + 26 x 27 x 28

3A = 26 x 27 x 28

A= \(\text{ }\frac{\text{26 x 27 x 28}}{3}=6552\)

Cậu học cấp 2 rồi còn giải bài cấp 1 làm chi.

giải chi tiết giúp mình

1 /(27x28) ,1/(28 x29)

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