bằng 2270/5049 đó bạn

\(\frac{5}{2.7}+\frac{5}{7.12}+\frac{5}{12.17}+\frac{5}{22.27}\)

\(=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{12}+\frac{1}{12}-\frac{1}{17}+\frac{5}{22.27}\)

\(=\frac{1}{2}-\frac{1}{17}+\frac{5}{22.27}\)

\(=\frac{2270}{5049}\)

D = 2 3 − 1 2 . 1 4 = 1 24 E = 2 3 − 1 2 . 1 4 =  13 24 F = 3 4 − 1 − 2 . 4 6 − 1 3 = 5 12

\(\dfrac{8}{5}\cdot\dfrac{45}{17}\cdot\dfrac{-25}{16}\cdot\dfrac{-34}{9}=\dfrac{8\cdot5\cdot9\cdot25\cdot17\cdot2}{5\cdot17\cdot8\cdot2\cdot9}=\dfrac{25}{9}\) (bỏ đi các dấu trừ vì số âm nhân số âm là số dương)

3-(17-x)=289-(36+289)

<=> 3-17+x=289-36-289

<=> -14+x=-36 => x=-22

25-(x+5)=-45-(15-45)

<=> 25-x-5=-45-15+45

<=> 20-x=-15=> x=35

34-(21-x)=(3747-30)-3747

<=> 334-21+x=3747-30-3747

<=> 313+x=-30=> x=-343

3 - ( 17 - x ) = 289 - ( 36 + 289 )

3 - 17 + x = 289 - 36 - 289

- 14 + x = - 36

          x = ( - 36 ) - ( - 14 )

          x= - 22

25 - ( x + 5 ) = - 45 - ( 15 - 45)

25 - x - 5 = - 45 - 15 + 45

20 - x = - 15

      x = 20 - ( - 15 )

      x = 35

34 - ( 21 - x ) = ( 3747 - 30 ) - 3747

34 - 21 + x = 3747 - 30 - 3747

13 + x = - 30

       x = ( - 30 ) - 13

       x = - 46

\(\left(\frac{5}{2.7}+\frac{5}{7.12}+\frac{5}{17.22}+\frac{5}{22.27}+\frac{5}{27.32}\right)x=945\)

\(\left(\frac{7-2}{2.7}+\frac{12-7}{7.12}+\frac{17-12}{12.17}+\frac{22-17}{17.22}+\frac{27-22}{22.27}+\frac{32-27}{27.32}\right)x=945\)

\(\left(\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{12}+...+\frac{1}{27}-\frac{1}{32}\right)x=945\)

\(\left(\frac{1}{2}-\frac{1}{32}\right)x=945\Leftrightarrow\frac{15}{32}x=945\Leftrightarrow x=945:\frac{15}{32}=2016\)

Bài 1: 

a) Ta có: \(x\left(x^2-4\right)=0\)

\(\Leftrightarrow x\left(x-2\right)\left(x+2\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x-2=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=2\\x=-2\end{matrix}\right.\)

Vậy: \(x\in\left\{0;2;-2\right\}\)

b) Ta có: \(\left(2x-3\right)+\left(-3x\right)-\left(x-5\right)=40\)

\(\Leftrightarrow2x-3-3x-x+5=40\)

\(\Leftrightarrow-2x+2=40\)

\(\Leftrightarrow-2x=38\)

hay x=-19

Vậy: x=-19

Bài 2: 

a) Ta có: \(-45\cdot12+34\cdot\left(-45\right)-45\cdot54\)

\(=-45\cdot\left(12+34+54\right)\)

\(=-45\cdot100\)

\(=-4500\)

b) Ta có: \(43\cdot\left(57-33\right)+33\cdot\left(43-57\right)\)

\(=43\cdot57-43\cdot33+43\cdot33-33\cdot57\)

\(=43\cdot57-33\cdot57\)

\(=57\cdot\left(43-33\right)\)

\(=57\cdot10=570\)

a ) x = − 3 4 + 4 5 ⇔ x = 1 20 b ) x = − 4 9 : 2 , 5 ⇔ x = − 8 45 c ) 3 , 5 − 2 x = 1 7 : 2 3 7 ⇔ 3 , 5 − 2 x = 1 17 ⇔ 2 x = 3 , 5 − 1 17 ⇔ 2 x = 117 34 ⇔ x = 117 34 : 2 = 117 68