(x+y)^2=(x+1)(x+2)
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(x^2+2xy+y^2=x^2+3x+2\)
\(\Leftrightarrow x^2-x^2+2xy+3x+y^2-2=0\)
\(\Leftrightarrow2xy+3x+y^2-2=0\)
P/s : chả hiểu đề bài :))
![](https://rs.olm.vn/images/avt/0.png?1311)
Vì AB // CD nên \(\hept{\begin{cases}\widehat{A}+\widehat{D}=180^0\\\widehat{B}+\widehat{C}=180^0\end{cases}}\)(định lí hình thang)
Mà \(\widehat{A}=5\widehat{D}\)=> \(\widehat{5D}+\widehat{D}=180^0\)=> \(6\widehat{D}=180^0\)=> \(\widehat{D}=30^0\)(1)
Thay (1) vào \(\widehat{A}=5\widehat{D}\)ta có :
\(\widehat{A}=5\cdot30^0=150^0\)
Lại có : \(\widehat{B}=4\widehat{C}\)
=> \(4\widehat{C}+\widehat{C}=180^0\)
=> \(5\widehat{C}=180^0\)
=> \(\widehat{C}=36^0\)(2)
Thay (2) vào \(\widehat{B}=4\widehat{C}\)ta có :
=> \(\widehat{B}=4\cdot36^0=144^0\)
Vậy : ^A = 1500 , ^B = 1440 , ^C = 360 , ^D = 300
![](https://rs.olm.vn/images/avt/0.png?1311)
a) 2( x - 1 )2 + ( x + 3 )2 = 3( x - 2 )( x + 1 )
<=> 2( x2 - 2x + 1 ) + x2 + 6x + 9 = 3( x2 - x - 2 )
<=> 2x2 - 4x + 2 + x2 + 6x + 9 = 3x2 - 3x - 6
<=> 2x2 - 4x + x2 + 6x - 3x2 + 3x = -6 - 2 - 9
<=> 5x = -17
<=> x = -17/5
b) ( x - 1 )2 - 2( x - 3 ) = ( x + 1 )2
<=> x2 - 2x + 1 - 2x + 6 = x2 + 2x + 1
<=> x2 - 2x - 2x - x2 - 2x = 1 - 1 - 6
<=> -6x = -6
<=> x = 1
c) ( x - 3 )3 - ( x - 3 )( x2 + 3x + 9 ) + 6( x + 1 )2 + 3x2 = -33
<=> x3 - 9x2 + 27x - 27 - ( x3 - 33 ) + 6( x2 + 2x + 1 ) + 3x2 = -33
<=> x3 - 9x2 + 27x - 27 - x3 + 27 + 6x2 + 12x + 6 + 3x2 = -33
<=> x3 - 9x2 + 27x - x3 + 6x2 + 12x + 3x2 = -33 - 27 + 27 - 6
<=> 39x = -39
<=> x = -1
a) Đặt \(a=x-1\)\(\Rightarrow\)\(\hept{\begin{cases}x+3=a+4\\x-2=a-1\\x+1=a+2\end{cases}}\)
Ta có: \(2a^2+\left(a+4\right)^2=3.\left(a-1\right)\left(a+2\right)\)
\(\Leftrightarrow2a^2+a^2+4a+4=3.\left(a^2+a-2\right)\)
\(\Leftrightarrow3a^2+4a+4=3a^2+3a-6\)
\(\Leftrightarrow a=-10\)
\(\Rightarrow x-1=-10\)
\(\Leftrightarrow x=-9\)
Vậy \(S=\left\{-9\right\}\)
b) Đặt \(b=x-1\)\(\Rightarrow\)\(\hept{\begin{cases}x-3=b-2\\x+1=b+2\end{cases}}\)
Ta có: \(b^2-2.\left(b-2\right)=\left(b+2\right)^2\)
\(\Leftrightarrow b^2-2b+4=b^2+4b+4\)
\(\Leftrightarrow-6b=0\)
\(\Leftrightarrow b=0\)
\(\Rightarrow x-1=0\)
\(\Leftrightarrow x=1\)
Vậy \(S=\left\{1\right\}\)
c) Ta có: \(\left(x-3\right)^3-\left(x-3\right)\left(x^2+3x+9\right)+6\left(x+1\right)^2+3x^2=-33\)
\(\Leftrightarrow\left(x-3\right)^3-\left(x-3\right)^3+6\left(x^2+2x+1\right)+3x^2+33=0\)
\(\Leftrightarrow6x^2+12x+6+3x^2+33=0\)
\(\Leftrightarrow9x^2+12x+39=0\)
\(\Leftrightarrow\left(9x^2+12x+4\right)+35=0\)
\(\Leftrightarrow\left(3x+2\right)^2+35=0\)
Vì \(\left(3x+2\right)^2\ge0\forall x\)\(\Rightarrow\)\(\left(3x+2\right)^2+35\ge35>0\forall x\)
mà \(\left(3x+2\right)^2+35=0\)
\(\Rightarrow\)\(\left(3x+2\right)^2+35=0\)vô nghiệm
Vậy \(S=\varnothing\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a. \(x\left(x-2\right)-x\left(x-1\right)\left(x-3\right)=0\)
\(\Leftrightarrow x^2-2x-x^3+4x^2-3x=0\)
\(\Leftrightarrow-x^3+5x^2-5x=0\)
\(\Leftrightarrow-x\left(x^2-5x+5\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}-x=0\\x^2-5x+5=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=0\\\left(x-\frac{5}{2}\right)^2-\frac{5}{4}=0\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x=0\\\left(x-\frac{5}{2}\right)^2=\frac{5}{4}\end{cases}\Leftrightarrow}\hept{\begin{cases}x=0\\x-\frac{5}{2}=\frac{\sqrt{5}}{2}\\x-\frac{5}{2}=-\frac{\sqrt{5}}{2}\end{cases}}\)
\(\Leftrightarrow\hept{\begin{cases}x=0\\x=\frac{5+\sqrt{5}}{2}\\x=\frac{5-\sqrt{5}}{2}\end{cases}}\)
a) \(x\left(x-2\right)-x\left(x-1\right)\left(x-3\right)=0\)
\(\Leftrightarrow x\left(x-2-x^2+4x-3\right)=0\)
\(\Leftrightarrow x\left(-x^2+5x-5\right)=0\)
\(\Leftrightarrow x\left(x-\frac{5+\sqrt{5}}{2}\right)\left(x-\frac{5-\sqrt{5}}{2}\right)=0\)
=> \(x\in\left\{0;\frac{5+\sqrt{5}}{2};\frac{5-\sqrt{5}}{2}\right\}\)
b) \(\left(2x-5\right)\left(x+3\right)-\left(x-1\right)\left(2x+3\right)=0\)
\(\Leftrightarrow2x^2+x-15-2x^2-x+3=0\)
\(\Leftrightarrow-12=0\left(vn\right)\)
c) \(\left(x-2\right)\left(x^2+2x+8\right)-x^3-2x+1=0\)
\(\Leftrightarrow x^3+4x-16-x^3-2x+1=0\)
\(\Leftrightarrow2x=15\)
\(\Rightarrow x=\frac{15}{2}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Vì \(\left(x^2-2^2\right)^2\ge0\Rightarrow\left(x^2-2^2\right)^2+2010\ge2010\)
\(\Leftrightarrow\frac{\left(x^2-2^2\right)+2010}{-2009}\le\frac{2010}{-2009}\)
Vậy Dmax=-2010/2009, dấu = xảy ra khi và chỉ khi \(x^2-2^2=0\Leftrightarrow x=\pm2\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) VT = x3 + 3x2y + 3xy2 + y3 + x3 - 3x2y + 3xy2 - y3
= 2x3 + 6xy2
= 2x( x2 + 3y2 ) = VP
=> đpcm
b) VT = x3 + 3x2y + 3xy2 + y3 - ( x3 - 3x2y + 3xy2 - y3 )
= x3 + 3x2y + 3xy2 + y3 - x3 + 3x2y - 3xy2 + y3
= 3x2y + 2y3
= 2y( 3x2 + y2 ) = VP
=> đpcm
a)
\(VT=\left(x+y+x-y\right)\left[\left(x+y\right)^2-\left(x+y\right)\left(x-y\right)+\left(x-y\right)^2\right]\)
\(=2x\left[x^2+2xy+y^2-x^2+y^2+x^2-2xy+y^2\right]\)
\(=2x\left(x^2+3y^2\right)=VP\)
b)
\(VT=\left(x+y-x+y\right)\left[\left(x+y\right)^2+\left(x+y\right)\left(x-y\right)+\left(x-y\right)^2\right]\)
\(=2y\left(x^2+2xy+y^2+x^2-y^2+x^2-2xy+y^2\right)\)
\(=2y\left(3x^2+y^2\right)=VP\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có: \(D=\frac{\left(x^2-2^2\right)+2010}{-2009}=\frac{x^2+2006}{-2009}=\frac{3-x^2}{2009}-1\)
Để D đạt GTLN => \(\frac{3-x^2}{2009}\) đạt GTLN, mà \(3-x^2\le3\left(\forall x\right)\)
Dấu "=" xảy ra khi: \(x=0\)
Vậy Max(D) = \(-\frac{2006}{2009}\) khi x = 0
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có :
\(VP=x^3+3x^2y+3xy^2+y^3-3x^2y-3xy^2\)
\(=x^3+y^3=\left(x+y\right)\left(x^2-xy+y^2\right)=VT\)
\(\RightarrowĐPCM\)
VT = x3 + y3 ( HĐT số 6 )
= x3 + 3x2y + 3xy2 + y3 - 3x2y - 3xy2
= ( x3 + 3x2y + 3xy2 + y3 ) - ( 3x2y + 3xy2 )
= ( x + y )3 - 3xy( x + y ) = VP
=> đpcm
\(\left(x+y\right)^2=\left(x+1\right)\left(x+2\right)\Leftrightarrow x^2+2xy+y^2=x^2+3x+2\)
\(\Leftrightarrow2xy-3x-2+y^2=0\)