Bài 3: 

a: x=-15

b: =>2x=18

hay x=9

1) \(ĐK:x\in R\)

2) \(ĐK:x< 0\)

3) \(ĐK:x\in\varnothing\)

4) \(=\sqrt{\left(x+1\right)^2+2}\) 

\(ĐK:x\in R\)

5) \(=\sqrt{-\left(a-4\right)^2}\)

\(ĐK:x\in\varnothing\)

Bài 1 : 

\(49\left(x-2\right)^2-25\left(2x+1\right)^2=0\)

\(\Leftrightarrow\left[7\left(x-2\right)-5\left(2x+1\right)\right]\left[7\left(x-2\right)+5\left(2x+1\right)\right]=0\)

\(\Leftrightarrow\left(7x-14-10x-5\right)\left(7x-14+10x+5\right)=0\)

\(\Leftrightarrow\left(-3x-19\right)\left(17x-9\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}-3x=19\\17x=9\end{cases}\Leftrightarrow\orbr{\begin{cases}x=\frac{-19}{3}\\x=\frac{9}{17}\end{cases}}}\)

Bài 2 : 

+) \(9x^2-6xy+y^2-21x+7y\)

\(=\left(3x-y\right)^2-7\left(3x-y\right)\)

\(=\left(3x-y\right)\left(3x-y-7\right)\)

+) \(x^2+2x-35\)

\(=x^2+2x+1-36\)

\(=\left(x+1-6\right)\left(x+1+6\right)\)

\(=\left(x-5\right)\left(x+7\right)\)

+) \(2x^2+9x-5\)

\(=2x^2-x+10x-5\)

\(=x\left(2x-1\right)+5\left(2x-1\right)\)

\(=\left(2x-1\right)\left(x+5\right)\)

+) \(6x^2+23x+15\)

\(=6x^2+18x+5x+15\)

\(=6x\left(x+3\right)+5\left(x+3\right)\)

\(=\left(x+3\right)\left(6x+5\right)\)

\(\left(2x+5\right)^2-2\left(2x+5\right)\left(x-1\right)+\left(x+1\right)^2=49\)

<=>\(\left\{\left(2x-5\right)-\left(x-1\right)\right\}^2=49\)

<=> \(\left(2x-5-x+1\right)^2=49\)

<=> \(\left(x-4\right)^2=49\)

<=> \(\hept{\begin{cases}x-4=7\\x-4=-7\end{cases}}\) 

<=> \(\hept{\begin{cases}x=11\\x=-3\end{cases}}\)

học tốt

5 + ( x + 27 ) = 64

a) \(\Rightarrow x+27=59\Rightarrow x=32\)

b) \(\Rightarrow x-2=39\Rightarrow x=41\)

c) \(\Rightarrow x+5=-322\Rightarrow x=-327\)

d) \(\Rightarrow5x=35\Rightarrow x=7\)

e) \(\Rightarrow4\left(x-5\right)=56\Rightarrow x-5=14\Rightarrow x=19\)

f) \(\Rightarrow15+x=37\Rightarrow x=22\)

g) \(\Rightarrow7\left(13-x\right)=35\Rightarrow13-x=5\Rightarrow x=8\)

h) \(\Rightarrow10\left(x+1\right)=100\Rightarrow x+1=10\Rightarrow x=9\)

a. Ta có: \(x^2-10x+26+y^2+2y=0\Leftrightarrow\left(x^2-10x+25\right)+\left(y^2+2y+1\right)=0\\ \)

\(\Leftrightarrow\left(x+5\right)^2+\left(y+1\right)^2=0\Rightarrow\hept{\begin{cases}x+5=0\\y+1=0\end{cases}\Leftrightarrow\hept{\begin{cases}x=-5\\y=-1\end{cases}}}\)

b. \(\left(2x+5\right)^2-\left(x-7\right)^2=0\Leftrightarrow\left(2x+5+x-7\right).\left(2x+5-x+7\right)=0\)

\(\Leftrightarrow\left(3x-2\right).\left(x+12\right)=0\Leftrightarrow\orbr{\begin{cases}3x-2=0\\x+12=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=\frac{2}{3}\\x=-12\end{cases}}}\)

c. \(25.\left(x-3\right)^2=49.\left(1-2x\right)^2\Leftrightarrow\left(5x-15\right)^2=\left(7-14x\right)^2\Leftrightarrow\left(5x-15\right)^2-\left(7-14x\right)^2=0\)

\(\Leftrightarrow\left(5x-15-7+14x\right).\left(5x-15+7-14x\right)=0\Leftrightarrow\left(19x-22\right).\left(-9x-8\right)=0\)

\(\Leftrightarrow\left(19x-22\right).\left(9x+8\right)=0\Leftrightarrow\orbr{\begin{cases}19x-22=0\\9x+8=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=\frac{22}{19}\\x=-\frac{8}{9}\end{cases}}}\)

d. \(\left(x+2\right)^2=\left(3x-5\right)^2\Leftrightarrow\left(x+2\right)^2-\left(3x-5\right)^2=0\Leftrightarrow\left(x+2+3x-5\right).\left(x+3-3x+5\right)=0\)

\(\Leftrightarrow\left(4x-3\right).\left(8-2x\right)=0\Leftrightarrow\orbr{\begin{cases}4x-3=0\\8-2x=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=\frac{3}{4}\\x=4\end{cases}}}\)

e. \(x^2-2x+1=16\Leftrightarrow\left(x-1\right)^2-16=0\Leftrightarrow\left(x-1-4\right).\left(x-1+4\right)=0\)

\(\Leftrightarrow\left(x-5\right).\left(x+3\right)=0\Leftrightarrow\orbr{\begin{cases}x-5=0\\x+3=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=5\\x=-3\end{cases}}}\)

Cảm ơn bn rất nhìu nha!!!^-^!!!

Bn ơi cho mik hỏi cái này đc ko ở câu a hai số cộng vs nhau bằng 0 thì một trong hai số đó là băng 0 à bn . Hi hi mik lại nghĩ là hai số nhân vs nhau bằng 0 thì 1 trong hai số đó ms bằng 0 chứ!!! Dù sao thì cx cảm ơn bn nhìu nà!!! Chúc bn học tốt nha!!!

(2x-25)=49 

2x - 25 = 49

2x = 49 - 25

2x = 24

x = 24 : 2

x = 12

tich nha bạn

2x - 25 = 49 

2x         = 49 - 25

2x        = 24

x          = 24 : 2

x          = 12

tick mk nha 

lộn đề

(2x-25)=49

2x - 25 = 49

2x = 49 + 25

2x = 74

x = 74 : 2

x = 37

**** mình nha 

a)   154-(x-4)=2*25

154-x+4=50

x+4=104

x=100

b)2346:(25+x)=23

25+x=102

x=77