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Ta có: \(\left(2x-1\right)\left(4x^2+2x+1\right)-2x\left(2x-3\right)\left(2x+3\right)=81x^2\)

=>\(8x^3-1-2x\left(4x^2-9\right)=81x^2\)

=>\(8x^3-1-8x^3+18x=81x^2\)

=>\(81x^2=18x-1\)

=>\(81x^2-18x+1=0\)

=>\(\left(9x-1\right)^2=0\)

=>9x-1=0

=>9x=1

=>\(x=\frac19\)

21 tháng 7

\(\left(2x-1\right)\left(4x^2+2x+1\right)-2x\left(2x-3\right)\left(2x+3\right)=81x^2\)

\(8x^3-1-2x\left(4x^2-9\right)=81x^2\)

\(8x^3-1-\left(8x^3-18x\right)=81x^2\)

\(8x^3-1-8x^3+18x=81x^2\)

\(18x-1=81x^2\)

\(81x^2-18x+1=0\)

\(\left(9x\right)^2-2\cdot9x+1=0\)

\(\left(9x-1\right)^2=0\)

\(9x-1=0\)

\(x=\frac19\)

Vậy \(x=\frac19\)

26 tháng 10 2018

phần b thay dấu = bằng dấu + nha

29 tháng 10 2022

a: \(=4x^2-9-4x^2-4x-1=-4x-10\)

b: \(\left(2x+1\right)^2+2\left(4x^2-1\right)+\left(2x-1\right)^2\)

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

\(=\left(2x+1+2x-1\right)^2=\left(4x\right)^2=16x^2\)

c: \(=8x^3+27-8x^3+2-2x=-2x+29\)

d: \(=x^3-6x^2y+12xy^2-8y^3-x^3+8y^3=-6x^2y+12xy^2\)

8 tháng 8 2018

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

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

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

\(x^3-4x^2+12x-27=x^3-3x^2-x^2+3x+9x-27\)

\(=x^2\left(x-3\right)-x\left(x-3\right)+9\left(x-3\right)\)

\(=\left(x-3\right)\left(x^2-x+9\right)\)

\(x^4+2x^3+2x^2+2x+1=x^4+x^2+2x^3+x^2+2x+1\)

\(=x^2\left(x^2+1\right)+2x\left(x^2+1\right)+\left(x^2+1\right)\)

\(=\left(x^2+1\right)\left(x^2+2x+1\right)\)

\(=\left(x^2+1\right)\left(x+1\right)^2\)

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

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

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

8 tháng 8 2018

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

                                    \(=x^2.\left(x+1\right)+x.\left(x+1\right)+\left(x+1\right)\)

                                   \(=\left(x+1\right).\left(x^2+x+1\right)\)

\(x^3-4x^2+12x-27\)

\(=\left(x^3-x^2\right)-\left(3x^2-3x\right)+\left(9x-27\right)\)

\(=x^2.\left(x-1\right)-3x.\left(x-1\right)+9.\left(x-3\right)\)

\(=\left(x-1\right).\left(x^2-3x\right)+9.\left(x-3\right)\)

\(=x.\left(x-1\right).\left(x-3\right)+9.\left(x-3\right)\)

\(=\left(x-3\right)\left[x.\left(x-1\right)+9\right]\)

b: \(\Leftrightarrow\dfrac{2}{\left(x+7\right)\left(x-3\right)}=\dfrac{3x+21}{\left(x-3\right)\left(x+7\right)}\)

=>3x+21=2

=>x=-19/3

d: \(\Leftrightarrow\left(2x+1\right)^2-\left(2x-1\right)^2=8\)

\(\Leftrightarrow4x^2+4x+1-4x^2+4x-1=8\)

=>8x=8

hay x=1

25 tháng 2 2020

1) \(\frac{x+1}{2x-2}+\frac{x^2+3}{2-2x^2}\)

\(=\frac{-4x^2+8x-4}{-4x^3+4x^2+4x-4}\)

\(=\frac{-x^2+2x-1}{-x^3+x^2+x-1}\)

\(=\frac{\left(-x+1\right)\left(x-1\right)}{\left(-x-1\right)\left(x-1\right)\left(x-1\right)}\)

\(=\frac{1}{x+1}\)

2) \(\frac{1-2x}{2x}+\frac{2x}{2x-1}+\frac{1}{2x-4x^2}\)

\(=\frac{-16x^3+16x^2-4x}{-16x^4+16x^3-4x^2}\)

\(=\frac{-16x^2+16x-4}{-16x^3+16x^2-4x}\)

\(=\frac{-4x^2+4x-1}{-4x^3+4x^2-x}\)

\(=\frac{\left(-2x+1\right)\left(2x-1\right)}{x\left(-2x+1\right)\left(2x-1\right)}\)

\(=\frac{1}{x}\)

25 tháng 9 2017

d)

x4 + x3 - 3x3 - 3x2 + 3x2 + 3x - x - 1

= x3 ( x + 1 ) - 3x2 ( x + 1 ) + 3x ( x+1) - (x +1)

= (x + 1)(x3 - 3x2 + 3x - 1)

= (x +1 )( x - 1 )3

25 tháng 9 2017

b)

x3+2x2+2x+1

= x3+x2+x2+x+x+1

= x2(x+1) + x(x + 1) + (x+1)

= (x + 1)( x2 + x + 1)

c)

x3-4x2+12x - 27

= x3-3x2-x2+3x+9x-27

= x2(x-3)-x(x-3)+9(x-3)

= (x-3)(x2-x+9)

8 tháng 9 2018

mấy cái này chỉ cần dùng hằng đẳng thức thui mà ..tự lm nha

27 tháng 2 2019

sorry em mới lớp 7

15 tháng 4 2019

lớp 7 kệ e chị có bắt e tl đâu

25 tháng 4 2017

a)\(\frac{4x+3}{5}-\frac{6x-2}{7}=\frac{5x+4}{3}+3\)

   \(84x+63-90x+30=175x+140+315\)

    93-6x=175x+455

     -362=181x

       x=-2

25 tháng 4 2017

b)\(9x^2-1=\left(3x+1\right)\left(4x+1\right)\)

   \(\left(3x-1\right)\left(3x+1\right)-\left(3x+1\right)\left(4x+1\right)=0\)

      \(\left(3x+1\right)\left(3x-1-4x-1\right)=0\)

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

\(\Rightarrow\orbr{\begin{cases}3x+1=0\\-x-2=0\end{cases}\Rightarrow}\orbr{\begin{cases}x=-\frac{1}{3}\\x=-2\end{cases}}\)

21 tháng 5 2021

\(\frac{4}{2x+3}-\frac{7}{3x-5}=0\left(đkxđ:x\ne-\frac{3}{2};\frac{5}{3}\right)\)

\(< =>\frac{4\left(3x-5\right)}{\left(2x+3\right)\left(3x-5\right)}-\frac{7\left(2x+3\right)}{\left(2x+3\right)\left(3x-5\right)}=0\)

\(< =>12x-20-14x-21=0\)

\(< =>2x+41=0< =>x=-\frac{41}{2}\left(tm\right)\)

21 tháng 5 2021

\(\frac{4}{2x-3}+\frac{4x}{4x^2-9}=\frac{1}{2x+3}\left(đk:x\ne-\frac{3}{2};\frac{3}{2}\right)\)

\(< =>\frac{4\left(2x+3\right)}{\left(2x-3\right)\left(2x+3\right)}+\frac{4x}{\left(2x-3\right)\left(2x+3\right)}-\frac{2x-3}{\left(2x+3\right)\left(2x-3\right)}=0\)

\(< =>8x+12+4x-2x+3=0\)

\(< =>10x=15< =>x=\frac{15}{10}=\frac{3}{2}\left(ktm\right)\)