a) Đặt x^2+2x+2=t

\(\frac{4}{t-1}+\frac{3}{t+1}=\frac{3}{2}\Leftrightarrow\frac{4t+4+3t-3}{t^2-1}=\frac{7t+1}{t^2-1}=\frac{3}{2}\)

\(\Leftrightarrow14t+2=3t^2-3\Leftrightarrow3t^2-14t-5=3t\left(t-5\right)+t-5=0\)\(\Leftrightarrow\left(t-5\right)\left(3t+1\right)=0\Rightarrow\left[\begin{matrix}t=5\\t=-\frac{1}{3}\left(loai\right)\end{matrix}\right.\)

Với t=5 ta có (x+1)^2=4\(\Rightarrow\left[\begin{matrix}x+1=2\\x+1=-2\end{matrix}\right.\Rightarrow\left\{\begin{matrix}x=1\\x=-3\end{matrix}\right.\)

\(1,\\ a,=7x^3-49x^2+21x\\ b,=x^2-x-42\\ c,=x^2-16x+64\\ d,=9x^2+12x+4\\ e,=x^2-16-25+10x-x^2=10x-41\\ 2,\\ a,\Rightarrow2\left(x-7\right)=19\\ \Rightarrow x-7=\dfrac{19}{2}\Rightarrow x=\dfrac{33}{2}\\ b,\Rightarrow4x^2-20x+25-4x^2+3x-2x=50\\ \Rightarrow-19x=25\Rightarrow x=-\dfrac{25}{19}\)

a, A= -3x² + 15x + 3x² - 12x -3x + 10

    A= 15x - 15x + 10

    A= 10

b, B= 4x³ - 28x² + 8x - 4x³ + 28x² - 8x + 20

    B= 20

 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

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

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

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

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

\(a)PT\Leftrightarrow4x^2-9-4x^2+20x+3x=0.\\ \Leftrightarrow23x=9.\\ \Leftrightarrow x=\dfrac{9}{23}.\\ b)PT\Leftrightarrow\left(2x+1\right)\left(4x-3\right)-\left(2x+1\right)\left(2x-1\right)=0.\\\Leftrightarrow\left(2x+1\right)\left(4x-3-2x+1\right)=0.\\ \Leftrightarrow\left(2x+1\right)\left(2x-2\right)=0.\\ \Leftrightarrow\left(2x+1\right)\left(x-1\right)=0. \)

\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{-1}{2}.\\x=1.\end{matrix}\right.\)

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