Phân tích đa thức thành nhân tử:(em làm luôn đấy,ko ghi lại đề)

\(\left(x^3+y^3\right)-\left(x+y\right)+3xy\left(x+y\right)\)

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

\(=\left(x+y\right)\left(x^2+2xy+y^2-1\right)\)\(=\left(x+y\right)\left[\left(x+y\right)^2-1^2\right]\)

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

\(8x^3+12x^2+6x+1=0.\)

\(\Leftrightarrow\left(2x\right)^3+3.\left(2x\right)^2.1+3.2x.1^2+1^3=0\)

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

\(\Leftrightarrow2x+1=0\)

\(\Leftrightarrow x=-\frac{1}{2}\)

\(2x^2+5x-3=0\Leftrightarrow\left(2x^2+6x\right)+\left(-x-3\right)=0\)

\(\Leftrightarrow2x\left(x+3\right)-\left(x+3\right)=0\Leftrightarrow\left(x+3\right)\left(2x-1\right)=0\)

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

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

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

\(\Leftrightarrow\orbr{\begin{cases}x+1=0\\x-3=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=-1\\x=3\end{cases}.}\)

\(\left(5x-1\right)+2\left(1-5x\right)\left(4+5x\right)+\left(5x+4\right)^2\)

\(=5x-1+2\left(4+5x-20x-25x^2\right)+25x^2+40x+16\)

\(=25x^2+45x+15+8+10x-40x-50x^2\)

\(=-25x^2+15x+23\)

\(\left(x-y\right)^3+\left(y+x\right)^3+\left(y-x\right)^3-3xy\left(x+y\right)\)

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

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

\(=x^3+3x^2y+3xy^2+y^3-3xy^2-3x^2y\)

\(=x^3+y^3\)

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

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

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

....

a) x^2 - 11x + 18 = 0 

=> x^2 - 2x - 9x + 18 = 0 

=> x ( x- 2 ) - 9 ( x- 2 ) = 0 

=> ( x- 9 )( x- 2 )= 0 

=> x- 9 = 0 hoặc x - 2 = 0 

=> x= 9 hoặc x = 2 

a) \(B=\left[\frac{21}{\left(x+3\right)\left(x-3\right)}+\frac{x-4}{x-3}-\frac{\left(x-1\right)}{x+3}\right]:\left(\frac{x+3-1}{x+3}\right)\)

ĐK: \(\hept{\begin{cases}x\ne3\\x\ne-3\end{cases}}\)

\(=\left[\frac{21+x-4-\left(x-1\right)\left(x-3\right)}{\left(x-3\right)\left(x+3\right)}\right]:\left(\frac{x+2}{x+3}\right)\)

\(=\left[\frac{21+x-4-x^2+3x+x-3}{\left(x+3\right)\left(x-3\right)}\right]\times\left(\frac{x+3}{x+2}\right)\)

\(=\left(\frac{-x^2+5x+14}{x-3}\right)\left(\frac{1}{x+2}\right)\)

\(=\frac{-\left(x^2+2x-7x-14\right)}{\left(x-3\right)\left(x+2\right)}\)

\(=\frac{-\left(x+2\right)\left(x-7\right)}{\left(x-3\right)\left(x+2\right)}\)

\(=\frac{7-x}{x-3}\)

b) \(\Rightarrow\orbr{\begin{cases}2x+1=5\\2x+1=-5\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=2\\x=-3\end{cases}}\)

Mà \(x\ne-3\)

\(\Rightarrow x=2\)

Thế \(x=2\)vào B ta được:

\(B=\frac{7-2}{2-3}=-5\)

c) \(B=\frac{7-x}{x-3}=\frac{-3}{5}\)

\(\Leftrightarrow5\left(7-x\right)=-3\left(x-3\right)\)

\(\Leftrightarrow35-5x+3x-9=0\)

\(\Leftrightarrow-2x=-26\)

\(\Leftrightarrow x=13\)

Vậy để \(B=\frac{-3}{5}\)thì \(x=13\)

d) B<0\(\Rightarrow\frac{7-x}{x-3}< 0\)

TH1: \(\hept{\begin{cases}7-x< 0\\x-3>0\end{cases}\Rightarrow\hept{\begin{cases}x>7\\x>3\end{cases}\Rightarrow}x>7}\)

TH2: \(\hept{\begin{cases}7-x>0\\x-3< 0\end{cases}\Rightarrow\hept{\begin{cases}x< 7\\x< 3\end{cases}\Rightarrow}x< 3}\)

Để B<0 thì x>7 hoặc x<3

a) \(B=\left(\frac{21}{x^2-9}-\frac{x-4}{3-x}-\frac{x-1}{3+x}\right):\left(1-\frac{1}{x+3}\right)\)         ĐKXĐ: x khác =-3; x khác -2

\(B=\frac{21+x^2-x-12-x^2+4x-3}{\left(x+3\right)\left(x-3\right)}:\frac{x+2}{x+3}\)

\(B=\frac{3x+6}{\left(x+3\right)\left(x-3\right)}:\frac{x+2}{x+3}\)

\(B=\frac{3\left(x+2\right)}{\left(x+3\right)\left(x-3\right)}\cdot\frac{x+3}{x+2}\)

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

b) bước đầu tiên ta phải tìm x:

 \(\left|2x+1\right|=5\)

TH1: 2x+1=5                      TH2: 2x+1=-5

            2x=4                                 2x=-6

          x=2 (nhận)                             x=-3 (loại)

thay x=2 vào biểu thức B, ta được:

\(B=\frac{3}{2-3}=\frac{3}{-1}=-3\)

vậy B=-3 tại x=2

c) Để \(B=-\frac{3}{5}\)thì \(\frac{3}{x-3}=-\frac{3}{5}\)

\(\Leftrightarrow-3\left(x-3\right)=15\)

\(\Leftrightarrow x-3=-5\)

\(\Leftrightarrow x=-2\)

vậy \(x=-2\)thì \(B=-\frac{3}{5}\)

d) để B<0 thì \(\frac{3}{x-3}< 0\Leftrightarrow x-3< 0\Leftrightarrow x< 3\)

vậy để B<0 thì x phải < 3 và x khác -3

khong co may tinh sao lam

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

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

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

\(\Leftrightarrow\left(2x+3\right)\left(4x^2+12x+9-x^2-3x-3\right)=0\)

\(\Leftrightarrow\left(2x+3\right)\left(3x^2+9x+6\right)=0\)

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

\(\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{3}{2}\\x=-1\\x=-2\end{matrix}\right.\)

1. x = -2;-1;0;1;2 

2. x = 4 

1.Vì |x|<3 nên x thuộc {2;-2;1;-1;0}

2. Để (x-3).(x-5)<0 thì hai x-3 và x-5 phải khác dấu.

=>x-3>0 và x-5<0

=>3<x<5

=> x=4

a) \(x^3=x^5\)

=> \(x^3-x^5=0\)

=> \(x^3\left(1-x^2\right)=0\)

=> \(\orbr{\begin{cases}x^3=0\\1-x^2=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=0\\x^2=1\end{cases}}\Rightarrow\orbr{\begin{cases}x=0\\x=\pm1\end{cases}}\)

b) \(4x\left(x+1\right)=x+1\)

=> \(4x^2+4x-x-1=0\)

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

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

c) \(x\left(x-1\right)-2\left(1-x\right)=0\)

=> \(x\left(x-1\right)-\left[-2\left(x+1\right)\right]=0\)

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

=> \(\left(x-1\right)\left(x+2\right)=0\Rightarrow\orbr{\begin{cases}x=1\\x=-2\end{cases}}\)

d) Kết quả ?

e) \(\left(x-3\right)^2+3-x=0\)

=> \(x^2-6x+9+3-x=0\)

=> \(x^2-7x+12=0\)

=> \(x^2-3x-4x+12=0\)

=> \(x\left(x-3\right)-4\left(x-3\right)=0\)

=> (x - 4)(x - 3) = 0

=> \(\orbr{\begin{cases}x=4\\x=3\end{cases}}\)

f) Tương tự