\((\)125-120\()\)x45

5x45=225

\(\dfrac{30x25x7x8}{75x8x12x14}\)=\(\dfrac{10\cdot1\cdot7\cdot1}{1\cdot1\cdot1\cdot12\cdot2}\)=\(\dfrac{70}{24}\)

Bài 1 :

(4/5 + 3/10 - 1/5) x 6 : 4/7

= 9/10 x 6 : 4/7

= 27/5 : 4/7

= 189/20

2007 x 76 - 75 x 2007 - 2007

= 2007 x (76 - 75 - 1)

= 2007 x 0

= 0

(47,5 + 8,6 x 4,5 - 105)

= 47,5 + 38,7 - 105

= 86,2 - 105

= -94/5

Bài 2 :

a) x : 2/3 = 10

           x = 10 x 2/3

           x = 20/3

theo cách đó tự làm

Hoctot

a: Ta có: \(100-7\left(x-5\right)=58\)

\(\Leftrightarrow7\left(x-5\right)=42\)

\(\Leftrightarrow x-5=6\)

hay x=11

b: Ta có: \(12\left(x-1\right):3=4^3+2^3\)

\(\Leftrightarrow12\left(x-1\right)=216\)

\(\Leftrightarrow x-1=18\)

hay x=19

a)3.5.7.9/5.7.3.6=23814

b)30.25.7.8/75.8.12.14=752640

câu 1 : ( 26 - 3x ) : 5 + 71 = 75

              ( 26 - 3x ) : 5 = 4

                 26 - 3x =20

                  3x = 26 - 20

                    3x=6

                      x=6: 3

                      x=2

C4: 100 - 7( 5 - x) = 58

      7( 5 -x ) = 100- 58

       7( 5 - x) =42

          5 - x = 42 : 7

          5 - x = 6

               x = -1 

1. \(\left(26-3x\right):5+71=75\)

\(\left(26-3x\right):=75-71\)

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

\(26-3x=4.5\)

\(26-3x=20\)

\(3x=26-20\)

\(3x=6\)

\(x=6:3\)

\(x=2\)

2. \(5^{x+1}=125=5^3\) 

\(x+1=3\Rightarrow x=2\)

3. B = {x​​ ϵ N/30 < x < 40}

B = {31;32;33;34;35;36;37;38;39;40}

4. \(100-7\left(5-x\right)=58\)

\(100-35+7x=58\)

\(-7x=100-35-58=7\)

\(x=-7:7\)

\(x=-1\)

\(1,\\ \left(x-7\right)^{x+1}-\left(x-7\right)^{x+11}=0\\ \Leftrightarrow\left(x-7\right)^{x+1}\left[1-\left(x-7\right)^{10}\right]=0\\ \Leftrightarrow\left[{}\begin{matrix}\left(x-7\right)^{x+1}=0\\\left(x-7\right)^{10}=1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x-7=0\\x-7=1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=7\\x=8\end{matrix}\right.\)

\(2,\\ a,\left|2x-3\right|>5\Leftrightarrow\left[{}\begin{matrix}2x-3< -5\\2x-3>5\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x< -1\\x>4\end{matrix}\right.\\ b,\left|3x-1\right|\le7\Leftrightarrow\left[{}\begin{matrix}3x-1\le7\\1-3x\le7\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x\le\dfrac{8}{3}\\x\ge-2\end{matrix}\right.\\ c,\cdot x< -\dfrac{3}{2}\\ \Leftrightarrow5-3x+\left(-2x-3\right)=7\Leftrightarrow2-5x=7\Leftrightarrow x=-1\left(ktm\right)\\ \cdot-\dfrac{3}{2}\le x\le\dfrac{5}{3}\\ \Leftrightarrow\left(5-3x\right)+\left(2x+3\right)=7\Leftrightarrow8-x=7\Leftrightarrow x=1\left(tm\right)\\ \cdot x>\dfrac{5}{3}\\ \Leftrightarrow\left(3x-5\right)+\left(2x+3\right)=7\Leftrightarrow5x-2=7\Leftrightarrow x=\dfrac{9}{5}\left(tm\right)\\ \Leftrightarrow S=\left\{1;\dfrac{9}{5}\right\}\)

Mai lam

a)\(x\cdot150+480=430+150\)

\(x\cdot150+480=580\)

\(x\cdot150=580-480=100\)

\(x=100:150=\frac{2}{3}\)

b) \(\frac{5}{9}:x=\frac{2}{5}\)

\(x=\frac{5}{9}:\frac{2}{5}=\frac{25}{18}=1\frac{7}{18}\)

~học tốt~.

\(x\cdot150+480=430+150\)

\(x\cdot150+480=580\)

               \(x\cdot150=580-480\)

               \(x\cdot150=100\)

                           \(x=150:100\)

                           \(x=\frac{3}{2}\)

\(\frac{5}{9}:x=\frac{2}{5}\)

       \(x=\frac{5}{9}:\frac{2}{5}\)

       \(x=\frac{5}{9}\cdot\frac{5}{2}\)

       \(x=\frac{25}{18}\)

Dấu \(\cdot\) là dấu nhân

x * 150 + 480 = 430 + 150

x  * 150 + 480 = 580

x * 150  = 100

x = 2/3

5/9 : x = 2/5

x = 25/18

Ta có S=1/2^2+1/3^2+1/4^2+...+1/9^2

<1/2²+1/2*3+1/3*4+....+1/8*9

=1/2²+1/2-1/3+1/3-1/4+....+1/8-1/9

=1/4+1/2-1/9=23/36<32/36=8/9 (♪)

Ta lại có S=1/2^2+1/3^2+1/4^2+...+1/9^2

>1/2²+1/3*4+1/4*5+....+1/9*10

=1/2²+1/3-1/4+1/4-1/5+........+1/9-1/10

=1/2²+1/3-1/10

=19/20>8/20=2/5 ( ♫)

Từ (♪)( ♫) cho ta đpcm