2

\(M=2y-3x\sqrt{y}+x^2=y-2x\sqrt{y}+x^2+y-x\sqrt{y}\\ =\left(\sqrt{y}-x\right)^2+\sqrt{y}\left(\sqrt{y}-x\right)\\ =\left(\sqrt{y}-x\right)\left(\sqrt{y}-x+\sqrt{y}\right)\\ =\left(\sqrt{y}-x\right)\left(2\sqrt{y}-x\right)\)

b

\(y=\dfrac{18}{4+\sqrt{7}}=\dfrac{18\left(4-\sqrt{7}\right)}{16-7}=\dfrac{72-18\sqrt{7}}{9}=\dfrac{72}{9}-\dfrac{18\sqrt{7}}{9}=8-2\sqrt{7}\\ =7-2\sqrt{7}.1+1=\left(\sqrt{7}-1\right)^2\)

Thế x = 2 và y = \(\left(\sqrt{7}-1\right)^2\) vào M được:

\(M=2\left(\sqrt{7}-1\right)^2-3.2.\sqrt{\left(\sqrt{7}-1\right)^2}+2^2\\ =2\left(8-2\sqrt{7}\right)-6.\left(\sqrt{7}-1\right)+4\\ =16-4\sqrt{7}-6\sqrt{7}+6+4\\ =26-10\sqrt{7}\)

1:

a: =>2x-2căn x+3căn x-3-5=2x-4

=>căn x-8=-4

=>căn x=4

=>x=16

b: \(\Leftrightarrow\left(\sqrt{x}-2\right)\left(x+2\sqrt{x}+4\right)-3\sqrt{x}\left(\sqrt{x}-2\right)=0\)

=>(căn x-2)(x-căn x+4)=0

=>căn x-2=0

=>x=4

`(x-1)^2-2(x-1)(2x+1)+(2x+1)^2`

`=(x-1-2x-1)^2`

`=(-x-2)^2`

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

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

Bài 1:

\(\left\{{}\begin{matrix}xy+2=2x+y\left(1\right)\\2xy+y^2+3y=6\left(2\right)\end{matrix}\right.\)

\(\left(1\right)\Rightarrow xy-y+2-2x=0\)

\(\Rightarrow y\left(x-1\right)-2\left(x-1\right)=0\)

\(\Rightarrow\left(x-1\right)\left(y-2\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}x=1\\y=2\end{matrix}\right.\)

Với \(x=1\). Thay vào (2) ta được:

\(2y+y^2+3y=6\)

\(\Leftrightarrow y^2+5y-6=0\)

\(\Leftrightarrow y^2+y-6y-6=0\)

\(\Leftrightarrow y\left(y+1\right)-6\left(y+1\right)=0\)

\(\Leftrightarrow\left(y+1\right)\left(y-6\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}y=-1\\y=6\end{matrix}\right.\)

Với \(y=2\). Thay vào (2) ta được:

\(2x.2+2^2+3.2=6\)

\(\Leftrightarrow4x+4+6=6\)

\(\Leftrightarrow x=-1\)

Vậy hệ phương trình đã cho có nghiệm (x,y) \(\in\left\{\left(1;-1\right),\left(1;6\right),\left(-1;2\right)\right\}\)

Bài 2:

\(f\left(x\right)=x^4+6x^3+11x^2+6x\)

\(=x\left(x^3+6x^2+11x+6\right)\)

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

\(=x\left[x^2\left(x+1\right)+5x\left(x+1\right)+6\left(x+1\right)\right]\)

\(=x\left(x+1\right)\left(x^2+5x+6\right)\)

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

\(=x\left(x+1\right)\left[x\left(x+3\right)+2\left(x+3\right)\right]\)

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

b) Ta có: \(f\left(x\right)+1=x\left(x+1\right)\left(x+2\right)\left(x+3\right)+1\)

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

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

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

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

Vì x là số nguyên nên \(f\left(x\right)+1\) là số chính phương.

a: \(x\left(x^3-4\right)+2x^3-4\)

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

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

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

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

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

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

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

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

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

Ta có \(\left(1+2x\right)\left(1-2x\right)-x\left(x+2\right)\left(x-2\right)\)

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

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

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

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

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

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

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

Nhớ tick đúng nha