(2 giờ 18 phút x 9+2,3 giờ x 6+138 phút x 5) : 10

= (     2,3 giờ    x 9 + 2,3 giờ x 6 +  2,3 giờ     ) : 10

= 2,3 giờ x (   9 + 6    )  : 10

= 2,3 giờ x       15          : 10

=            34,5  giờ          :  10

=        3,45 giờ

a)  3x – 15 = 25 – 5x 

=> 3x + 5x = 25 + 15

=> 8x = 40

=> x = 5

 b) 3x - 17 = 2x – 7     

=> 3x - 2x = -7 + 17

=> x = 10

 c) 2x – 17 =  – (3x – 18)

=> 2x - 17 = -3x + 18

=> 2x + 3x = 18 + 17

=> 5x = 35

=> x = 7

d) 3x – 14 = 2(x – 9) + 1

=> 3x - 14 = 2x - 18 + 1

=> 3x - 2x = -18 + 1 + 14

=> x = -3

f) (x – 5)² = 9          

\(\Rightarrow\left[{}\begin{matrix}x-5=3\\x-5=-3\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=8\\x=2\end{matrix}\right.\)

a) Ta có: \(3x-15=25-5x\)

\(\Leftrightarrow3x-15-25+5x=0\)

\(\Leftrightarrow8x-40=0\)

\(\Leftrightarrow8x=40\)

hay x=5

Vậy: x=5

b) Ta có: \(3x-17=2x-7\)

\(\Leftrightarrow3x-17-2x+7=0\)

\(\Leftrightarrow x-10=0\)

hay x=10

Vậy: x=10

c) Ta có: \(2x-17=-\left(3x-18\right)\)

\(\Leftrightarrow2x-17=-3x+18\)

\(\Leftrightarrow2x-17+3x-18=0\)

\(\Leftrightarrow5x-35=0\)

\(\Leftrightarrow5x=35\)

hay x=7

Vậy: x=7

d) Ta có: \(3x-14=2\left(x-9\right)+1\)

\(\Leftrightarrow3x-14=2x-18+1\)

\(\Leftrightarrow3x-14-2x+18-1=0\)

\(\Leftrightarrow x+3=0\)

\(\Leftrightarrow x=-3\)

Vậy: x=-3

f) Ta có: \(\left(x-5\right)^2=9\)

\(\Leftrightarrow\left[{}\begin{matrix}x-5=3\\x-5=-3\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=8\\x=2\end{matrix}\right.\)

Vậy: \(x\in\left\{2;8\right\}\)

Bài 2. Tìm x, biết :                                

a) \(3x-15=25-5x\)

\(\Leftrightarrow8x=40\)

\(\Leftrightarrow x=5\)

Vậy x = 5

b) \(3x-17=2x-7\)

\(\Leftrightarrow x=10\)

Vậy x = 10

c) \(2x-17=-\left(3x-18\right)\)

\(\Leftrightarrow2x-17=18-3x\)

\(\Leftrightarrow5x=35\)

\(\Leftrightarrow x=7\)

Vậy x = 7

d) \(3x-14=2\left(x-9\right)+1\)

\(\Leftrightarrow3x-14=2x-18+1\)

\(\Leftrightarrow3x-14=2x-17\)

\(\Leftrightarrow x=-3\)

Vậy x = -3

e) \(\left(x-5\right)^2=9\)

\(\Rightarrow\left[{}\begin{matrix}x-5=3\\x-5=-3\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=8\\x=2\end{matrix}\right.\)

Vậy x = {8; 2}

14 : ( x - 17 ) = 2

(x-17) = 14 :2

x-17 = 7

x = 7+17

x = 24

14 : ( x - 17 ) = 2

         x - 17   = 14 : 2

         x - 17    = 7

          x          = 7 + 17

           x         = 24

Ta có : \(14:\left(x-17\right)=2\)

\(\Rightarrow x-7=14:2\)

\(\Rightarrow x-7=7\)

\(\Rightarrow x=14\)

a,-13+x=39            b,3x+17=14              

x=52                    x=-1

hok tốt

a) \(-13+x=39\)

\(\Leftrightarrow x=52\)

Vậy x=52

b) \(3x-\left(-17\right)=14\)

\(\Leftrightarrow3x+17=14\)

\(\Leftrightarrow3x=-3\)

\(\Leftrightarrow x=-1\)

\(c)|x+9|\cdot2=10\)

\(\Leftrightarrow|x+9|=5\)

\(\Leftrightarrow\orbr{\begin{cases}x+9=5\\x+9=-5\end{cases}\Leftrightarrow\orbr{\begin{cases}x=4\\x=-14\end{cases}}}\)

a,-13+x=39

          x = 39 - (-13)

          x = 39 + 13

          x = 52. 

b,3x-(-17)=14

   3x + 17 = 14

    3x        = 14 - 17

    3x        = -3

      x        = (-3) : 3

     x         = -1.

\(\text{c,|x+9|.2=10}\)

    \(|x+9|\)= 10 : 2

  \(|x+9|\) = 5

\(\Rightarrow\orbr{\begin{cases}x+9=5\\x+9=-5\end{cases}}\)\(\Rightarrow\orbr{\begin{cases}x=-4\\x=-14\end{cases}}\)

Hok tốt !

Ta có : 9(x + 1)² - (3x - 2)(3x + 2) = 10

=> 9(x² + 2x + 1) - (9x² - 4) = 10

=> 9x² + 18x + 9 - 9x² + 4 = 10

=> 9x² - 9x² + 18x + 13 = 10

=> 18x = 10 - 13

=> 18x = -3 

=> x = \(-\frac{1}{6}\)

Ta có : 9(x + 1)² - (3x - 2)(3x + 2) = 10

=> 9(x² + 2x + 1) - (9x² - 4) = 10

=> 9x² + 18x + 9 - 9x² + 4 = 10

=> 9x² - 9x² + 18x + 13 = 10

=> 18x = 10 - 13

=> 18x = -3 

=> x = \(-\frac{1}{6}\)

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 + 14 + 15 + 16 + 17+18 = 171 nhé

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 + 14 + 15 + 16 + 17+18.  = 171