2.(x-3)+5.(x+4)=49

2x-6+5x+20=49

2x+5x=49-20+6=35

7x=35

x=\(\dfrac{35}{7}\)=5

vậy

     2 ( x – 3 ) + 5 ( x + 4 ) = 49

               2x - 6 + 5x + 20 = 49

                            7x + 14 = 49

                           7x          = 35

                             x          = 5

Ta có: \(2\left(x-3\right)+5\left(x+4\right)=49\)

\(\Leftrightarrow7x=35\)

hay x=5

 Tìm x biết: 2 ( x - 3 ) +  5 ( x + 4 ) = 49

<=> 2x - 6 + 5x +20 = 49

<=> 2x+ 5x = 49 + 6  -20

<=> 7x = 35

<=> x = 35:7

<=> x = 5

x = 5 nha

a) \(\Leftrightarrow x^2-4x-x^2+6x-9=0\\ \Leftrightarrow2x=9\\ \Leftrightarrow x=4,5\)

b) \(\Leftrightarrow x^2-3x-10=0\\ \Leftrightarrow\left(x^2+2x\right)-\left(5x+10\right)=0\\ \Leftrightarrow x\left(x+2\right)-5\left(x+2\right)=0\\ \left(x-5\right)\left(x+2\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=5\\x=-2\end{matrix}\right.\)

c) \(\Leftrightarrow\left(2x-3-7\right)\left(2x-3+7\right)=0\\ \Leftrightarrow\left(2x-10\right)\left(2x+4\right)=0\\ \Leftrightarrow\left(x-5\right)\left(x+2\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=5\\x=-2\end{matrix}\right.\)

d) \(\Leftrightarrow\left(2x+7\right)\left(x-5\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{7}{2}\\x=5\end{matrix}\right.\)

Ta có: (2x)² -2.2x.3 +3² - 4.(x² - 1²) = 49

⇒4x² - 12x + 9 - 4x² + 4 = 49

⇒-12x = 49 - 9 - 4

⇒-12x = 36

⇒x = -3

\(\left(2x-3\right)^2-4\left(x-1\right)\left(x+1\right)=49\)
\(\Leftrightarrow\left[\left(2x\right)^2-2.2x.3+3^2\right]-4\left(x^2-1^2\right)=49\)
\(\Leftrightarrow4x^2-12x+9-4x^2+4=49\)
\(\Leftrightarrow-12x+13=49\)
\(\Leftrightarrow-12x=36\)
\(\Leftrightarrow x=-3\)
\(\text{Vậy }x=-3\)

\(\left(2x-3\right)^2-4\left(x-1\right)\left(x+1\right)=49\)

\(\Leftrightarrow4x^2-12x+9-4\left(x^2-1\right)=49\)

\(\Leftrightarrow4x^2-12x+9-4x^2+4=49\)

\(\Leftrightarrow-12x=49-9-4=36\)

\(\Leftrightarrow x-3\)

a, => 3^x.(1+3+3^2)-1 = 1052

=> 3^x.13 = 1052+1 = 1053

=> 3^x = 1053 : 13

=> 3^x = 81 = 3^4

=> x = 4

b, => x^2-49 >=0 ; 81-x^2 >=0 hoặc x^2-49 < = 0 ; 81-x^2 < = 0

=> 49 < = x^2 < = 81

=> -9 < = x < = -7 hoặc 7 < = x < = 9

=> x thuộc {-9;-8;-7;7;8;9}

Tk mk nha

Cảm ơn bạn nhiều nha^^ !

như cức

a) \(x:\frac{2}{3}=150\) 

\(x=150.\frac{2}{3}\) 

\(x=100\) 

b) \(\frac{35}{9}:x=\frac{35}{6}\) 

\(x=\frac{35}{9}.\frac{6}{35}=\frac{2}{3}\) 

c,d tương tự

a )  x : 2/3 = 150                                               c ) x : 4/7 = 180

     x         =    150 x 2/3                                        x         =    180 x  4/7

     x         =       100                                             x         =            720/7

b ) 35/9 : x  = 35/6                                             d )      49/8 : x  = 49/5 

              x  =  35/9 : 35/6                                                      x  =   49/8 : 49/5

             x   =     2/3                                                              x  =   5/8        

a) x : \(\frac{2}{3}\)= 150

   x = 150 x \(\frac{2}{3}\)

   x = 100

b) \(\frac{35}{9}:x=\frac{35}{6}\)

    x = \(\frac{35}{9}\): \(\frac{35}{6}\)

x = \(\frac{2}{3}\)

c) x : 4/7 = 180

x = 180 x 4/7

x = 720/7

d) 49/8 : x = 49/5

x = 49/8 : 49/5

x = 5/8

nhớ k cho mik nha mik đang rất cần cái k của bn

Giúp mình với 

a ) x = 1 3 . b ) x = 22 15 . c ) x = 50 9 . d ) x = 5 19 .