\(1,\Leftrightarrow7x=42\Leftrightarrow x=6\\ 2,\Leftrightarrow36-4x=4\Leftrightarrow4x=32\Leftrightarrow x=8\\ 3,\Leftrightarrow3x=35\Leftrightarrow x=\dfrac{35}{3}\\ 4,\Leftrightarrow x-12=144\Leftrightarrow x=156\\ 5,\Leftrightarrow x-14=16\Leftrightarrow x=30\\ 6,\Leftrightarrow3x-24=\dfrac{148}{73}\Leftrightarrow3x=\dfrac{1900}{73}\Leftrightarrow x=\dfrac{1900}{219}\\ 7,\Leftrightarrow33+x=45\Leftrightarrow x=12\\ 8,Sai.đề\\ 9,\Leftrightarrow\left(x+9\right):2=39\Leftrightarrow x+9=78\Leftrightarrow x=69\\ 11,\Leftrightarrow2\left(x+7\right)=38\Leftrightarrow x+7=19\Leftrightarrow x=12\\ 13,\Leftrightarrow2\left(x-51\right)=66\Leftrightarrow x-51=33\Leftrightarrow x=84\)

\(15,\Leftrightarrow x-19=9\Leftrightarrow x=28\\ 17,\Leftrightarrow\left(x-3\right):2=48\Leftrightarrow x-3=96\Leftrightarrow x=99\\ 19,\Leftrightarrow0x=46\Leftrightarrow x\in\varnothing\\ 8,Sai.đề\\ 14,\Leftrightarrow2x=209\Leftrightarrow x=\dfrac{209}{2}\\ 16,\Leftrightarrow2x+6=157\Leftrightarrow2x=151\Leftrightarrow x=\dfrac{151}{2}\\ 18,\Leftrightarrow5\left(x+4\right)=100\Leftrightarrow x+4=20\Leftrightarrow x=16\\ 20,\Leftrightarrow\left(3x-5\right)^3=27=3^3\Leftrightarrow3x-5=3\Leftrightarrow x=\dfrac{8}{3}\)

a) x² - 4x - 5 = 0

=> x² - 5x + x - 5 = 0

=> x(x - 5) + (x - 5) = 0

=> (x + 1)(x - 5) = 0

=> \(\orbr{\begin{cases}x+1=0\\x-5=0\end{cases}}\)

=> \(\orbr{\begin{cases}x=-1\\x=5\end{cases}}\)

b) 4x² + 7x - 11 = 0

=> 4x² + 11x - 4x - 11 = 0

=> x(4x + 11) - (4x + 11) = 0

=> (x - 1)(4x + 11) = 0

=> \(\orbr{\begin{cases}x-1=0\\4x+11=0\end{cases}}\)

=> \(\orbr{\begin{cases}x=1\\x=-\frac{11}{4}\end{cases}}\)

c) -7x² + 6x + 1 = 0

=> -7x² + 7x - x + 1 = 0

=> -7x(x - 1) - (x - 1) = 0

=> (-7x - 1)(x - 1) = 0

=> \(\orbr{\begin{cases}-7x-1=0\\x-1=0\end{cases}}\)

=> \(\orbr{\begin{cases}-7x=1\\x=1\end{cases}}\)

=> \(\orbr{\begin{cases}x=-\frac{1}{7}\\x=1\end{cases}}\)

d) -10x² + 7x + 3 = 0

=> -10x² + 10x - 3x + 3 = 0

=> -10x(x - 1) - 3(x - 1) = 0

=> (-10x - 3)(x - 1) = 0

=> \(\orbr{\begin{cases}-10x-3=0\\x-1=0\end{cases}}\)

=> \(\orbr{\begin{cases}-10x=3\\x=1\end{cases}}\)

=> \(\orbr{\begin{cases}x=-\frac{3}{10}\\x=1\end{cases}}\)

\(a,x^2-4x-5=0\)

\(\Rightarrow x^2-5x+x-5=0\)

\(\Rightarrow x\left(x-5\right)+\left(x-5\right)=0\)

\(\Rightarrow\left(x-5\right)\left(x+1\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x-5=0\\x+1=0\end{cases}\Rightarrow\orbr{\begin{cases}x=5\\x=-1\end{cases}}}\)

\(b,4x^2+7x-11=0\)

\(\Rightarrow4x^2-4x+11x-11=0\)

\(\Rightarrow4x\left(x-1\right)+11\left(x-1\right)=0\)

\(\Rightarrow\left(x-1\right)\left(4x+11\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x-1=0\\4x+11=0\end{cases}\Rightarrow\orbr{\begin{cases}x=1\\x=-\frac{11}{4}\end{cases}}}\)

\(c,-7x^2+6x+1=0\)

\(\Rightarrow-7x^2+7x-x+1=0\)

\(\Rightarrow-7x\left(x-1\right)-\left(x-1\right)=0\)

\(\Rightarrow\left(x-1\right)\left(-7x-1\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x-1=0\\-7x-1=0\end{cases}\Rightarrow\orbr{\begin{cases}x=1\\x=-\frac{1}{7}\end{cases}}}\)

\(d,-10x^2+7x+3=0\)

\(\Rightarrow-10x^2+10x-3x+3=0\)

\(\Rightarrow-10x\left(x+1\right)-3\left(x+1\right)=0\)

\(\Rightarrow\left(x+1\right)\left(-10x-3\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x+1=0\\-10x-3=0\end{cases}\Rightarrow\orbr{\begin{cases}x=-1\\x=-\frac{3}{10}\end{cases}}}\)

 ban nao giup minh vs mjnh vs

1. a) 7x² - 5x - 2 = 7x² - 7x + 2x - 2 = 7x(x - 1) + 2(x - 1) = (x - 1).(7x + 2)

2. 5(2x - 1)² - 3(2x - 1) = 0

<=> (2x - 1).[5(2x - 1) - 3] = 0

<=> (2x - 1).(10x - 8) = 0

<=> (2x - 1) = 0 hoặc (10x - 8) = 0

<=> x = 1/2 hoặc x = 4/5

3. x² - 4x + 7 = (x² - 4x + 4) + 3 = (x - 2)² + 3

Do: (x - 2)² > hoặc = 0 (với mọi x)

Nên (x - 2)² + 3 > hoặc = 3 (với mọi x)

Hay (x - 2)² + 3 > 0 (với mọi x)  => đpcm

\(7x^2-5x-2\)

\(=7x^2-7x+2x-2\)

\(=7x\left(x-1\right)+2\left(x-1\right)\)

\(=\left(x-1\right)\left(7x+2\right)\)

a) 2x(x - 5) - 2x² = 2x² - 10x - 2x² = -10x = 20 => x = 20 : (-10) = -2

b) 5x(2x - 7) + 2x(8 - 5x) = 10x² - 35x + 16x - 10x² = -19x = 5 => x = \(\frac{5}{-19}=\frac{-5}{19}\)

c) 4x(7x - 5) - 7x(4x - 2) = 28x² - 20x - 28x² + 14x = -6x = -12 => x = -12 : (-6) = 2

MK mới học lớp 7 thôi nhưng mk làm vài câu nha

a) 2x(x-5)-2x²=20

    2x²-100x-2x²=20

    100x=20

     x=20:100

      x=\(\frac{1}{5}\)

a) Ta có : 2x ( x - 5 ) - 2x² = 20

=> 2x ( x - 5 ) - 2x.x = 20

=> 2 x ( x - 5 - x ) = 20

=> 2x . ( -5 ) = 20

=> -10 x = 20

=> x = -2

Chọn mik mik làm tiếp

Hãy tích cho tui đi

vì câu này dễ mặc dù tui ko biết làm 

Yên tâm khi bạn tích cho tui

Tui sẽ ko tích lại bạn đâu

THANKS

( x +1 ) ( x + 4 ) = 5 căn ( x^2 + 5x +28 ) (1) 
= ( x + 1 ) ( x + 4 ) = 5 căn [ (x^2 + 5x + 4) + 24 ] 
= ( x + 1 ) ( x + 4 ) = 5 căn [ ( x + 1 ) ( x + 4 ) + 24 ] 
Đặt a = ( x + 1 ) ( x + 4 ) 
(1) <=> a = 5 căn ( a + 24 ) 
<=> a^2 = 25 ( a + 24 ) 
<=> a^2 - 25a - 600 = 0 
<=> a1 = 40 
a2 = -15 

với a = 40 ta có: 
( x + 1 ) ( x + 4 ) = 40 
<=> x^2 + 5x + 4 = 40 
<=> x^2 + 5x - 36 = 0 
<=> x = 4 và x = - 9 

với a = -15, ta có: 
( x + 1 ) ( x + 4 ) = -15 
<=> x^2 + 5x + 4 = -15 
<=> x^2 + 5x + 19 = 0 
delta < 0 => pt vô nghiệm 

Vậy s = { -9; 4}

a) \(58+7x=100\)

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

\(=>7x=42\)

\(=>x=42:7\)

\(=>x=6\)

b) \(3x-7=28\)

\(=>3x=28+7\)

\(=>3x=35\)

\(=>x=35:3\)

\(=>x=\dfrac{35}{3}\)

c) \(x-56:4=16\)

\(=>x-14=16\)

\(=>x=16+14\)

\(=>x=30\)

d) \(101+\left(36-4x\right)=105\)

\(=>36-4x=105-101\)

\(=>36-4x=4\)

\(=>4x=36-4\)

\(=>4x=32\)

\(=>x=32:4\)

\(=>x=8\)

e) \(\left(x-12\right):12=12\)

\(=>x-12=12.12\)

\(=>x-12=144\)

\(=>x=144-12\)

\(=>x=132\)

f) \(\left(3x-2^4\right).7^3=2.7^4\)

\(=>3x-2^4=2.7^4:7^3\)

\(=>3x-16=2.7=14\)

\(=>3x=14+16\)

\(=>3x=30\)

\(=>x=30:3\)

\(=>x=10\)

i) \(\left(10+2x\right).4^{2011}=4^{2013}\)

\(=>10+2x=4^{2013}:4^{2011}\)

\(=>10+2x=4^2=16\)

\(=>2x=16-10\)

\(=>2x=6\)

\(=>x=6:2\)

\(=>x=3\)

\(#WendyDang\)

`7x^2+7x=\sqrt{(4x+9)/28}`
Nhân 2 vế của pt cho 28 ta có:
`196x^2+196x=2\sqrt{28x+63}`
`<=>196x^2+224x+64=28x+63+2\sqrt{28x+63}+1`
`<=>(14x+8)^2=(\sqrt{28x+63}+1)^2`
Đến đây chai 2 trường hợp rồi giải thôi :D