giải hằng đẳng thức rồi rút gọn tìm x nhé

<=>x^3-6x^2+12x-8-x^3+6x^2=7

<=>12x=15

<=> x=5/4

chúc bạn hk tốt

\(6x^2-\left(2x+5\right)\left(3x-2\right)=7.\)

\(6x^2-\left(6x^2-4x+15x-10\right)=7\)

\(6x^2-6x^2+4x-15x+10=7\)

\(-11x+10=7\)

\(-11x=-3\)

\(x=\frac{-3}{-11}=\frac{3}{11}\)

\(6x^2-\left(2x+5\right)\left(3x-2\right)=7\)

\(6x^2-\left(6x^2-4x+15x-10\right)=7\)

+ Áp dụng quy tắc bở ngoặc ta có :

\(6x^2-6x^2+4x-15x+10=7\)

\(-11x+10=7\)

        \(-11x=7-10\)

            \(-11x=-3\)

                        \(x=-3:-11\)

                         \(x=\frac{-3}{-11}\)

                       \(\Rightarrow x=\frac{3}{11}\)

     Vậy \(x=\frac{3}{11}\)

Chúc bạn học tốt !!!

17 - x = 7 - 6x

6x - x = 7 - 17

5x = - 10

x = - 10 : 5

x = - 2

a)\(2x^4-6x^3+x^2+6x-3=0\)

\(\Leftrightarrow2x^4-6x^3+3x^2-2x^2+6x-3=0\)

\(\Leftrightarrow x^2\left(2x^2-6x+3\right)-\left(2x^2-6x+3\right)=0\)

\(\Leftrightarrow\left(x^2-1\right)\left(2x^2-6x+3\right)=0\)

\(\Leftrightarrow\left(x-1\right)\left(x+1\right)\left(2x^2-6x+3\right)=0\)

\(\Leftrightarrow\left[\begin{array}{nghiempt}x-1=0\\x+1=0\\2x^2-6x+3=0\end{array}\right.\)\(\Leftrightarrow\left[\begin{array}{nghiempt}x=1\\x=-1\\\Delta_{2x^2-6x+3}=\left(-6\right)^2-4\left(2.3\right)=12\end{array}\right.\)

\(\Leftrightarrow\left[\begin{array}{nghiempt}x=1\\x=-1\\x_{1,2}=\frac{6\pm\sqrt{12}}{4}\end{array}\right.\)

b)\(x^3+9x^2+26x+24=0\)

\(\Leftrightarrow x^3+5x^2+6x+4x^2+20x+24=0\)

\(\Leftrightarrow x\left(x^2+5x+6\right)+4\left(x^2+5x+6\right)=0\)

\(\Leftrightarrow\left(x^2+5x+6\right)\left(x+4\right)=0\)

\(\Leftrightarrow\left(x+2\right)\left(x+3\right)\left(x+4\right)=0\)

\(\Leftrightarrow\left[\begin{array}{nghiempt}x+2=0\\x+3=0\\x+4=0\end{array}\right.\)\(\Leftrightarrow\left[\begin{array}{nghiempt}x=-2\\x=-3\\x=-4\end{array}\right.\)

1) 5x - 7 = -21 - 2x

=> 5x + 2x = -21 + 7

=> 7x = -14

=> x = -2

2) x + 15 = 20 - 4x 

=> x + 4x = 20 - 15

=> 5x = 5

=> x = 1

3) 17 - x = 7 - 6x 

=> 17 - 7 = -6x + x

=> 10 = -5x

=> x = -2

1) 5x - 7 = -21 - 2x

-2x - 5x = -7 + 21

-7x = 14

=> x = -2

2) x+  15 = 20 - 4x

-4x - x = 15-  20

-5x = -5

x = 1

3) 17 - x = 7 - 6x

-6x + x = 17 - 7

-5x = 10 

x = -2