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\(4x^2+6xy+y^2\)
\(=\left(9x^2+6xy+y^2\right)-8x^2\)
\(=\left(3x+y\right)^2-8x^2\)
\(=\left(3x+y-\sqrt{8}x\right)\left(3x+y+\sqrt{8}x\right)\)
\(4x^2+6xy+y^2\)
\(=\left(9x^2+6xy+y^2\right)-5x^2\)
\(=\left(3x+y\right)^2-5x^2\)
\(=\left(3x+y+\sqrt{5}x\right)\left(3x+y-\sqrt{5}x\right)\)
Lời giải:
$x^4-x^3-2x-4=(x^4+x^3)-(2x^3+2x^2)+(2x^2+2x)-(4x+4)$
$=x^3(x+1)-2x^2(x+1)+2x(x+1)-4(x+1)$
$=(x+1)(x^3-2x^2+2x-4)$
$=(x+1)[x^2(x-2)+2(x-2)]=(x+1)(x-2)(x^2+2)$
#)Giải :
\(x^3-2x-4\)
\(=x^3+2x^2-2x^2+2x-4x-4\)
\(=x^3+2x^2+2x-2x^2-4x-4\)
\(=x\left(x^2+2x+2\right)-2\left(x^2+2x+2\right)\)
\(=\left(x-2\right)\left(x^2+2x+2\right)\)
\(x^4+2x^3+5x^2+4x-12\)
\(=x^4+x^3+6x^2+x^3+x^2+6x-2x^2-2x-12\)
\(=x^2\left(x^2+x+6\right)+x\left(x^2+x+6\right)-2\left(x^2+x+6\right)\)
\(=\left(x^2+x+6\right)\left(x^2+x-2\right)\)
\(=\left(x^2+x+6\right)\left(x-1\right)\left(x+2\right)\)
Câu 1.
Đoán được nghiệm là 2.Ta giải như sau:
\(x^3-2x-4\)
\(=x^3-2x^2+2x^2-4x+2x-4\)
\(=x^2\left(x-2\right)+2x\left(x-2\right)+2\left(x-2\right)\)
\(=\left(x-2\right)\left(x^2+2x+2\right)\)
\(1,=x\left(x^2-2x+1-y^2\right)=x\left[\left(x-1\right)^2-y^2\right]=x\left(x-y-1\right)\left(x+y-1\right)\\ 2,=\left(x+y\right)^3\\ 3,=\left(2y-z\right)\left(4x+7y\right)\\ 4,=\left(x+2\right)^2\\ 5,Sửa:x\left(x-2\right)-x+2=0\\ \Leftrightarrow\left(x-2\right)\left(x-1\right)=0\Leftrightarrow\left[{}\begin{matrix}x=1\\x=2\end{matrix}\right.\)
x4y4+64=x4y4+16x2y2+64-16x2y2
=(x2y2+8)2-16x2y2
=(x2y2-4xy+8)(x2y2+4xy+8)
\(x^4.y^4+4\)
\(=\left(x^4y^4-2x^3y^3+2x^2y^2\right)+\left(2x^3y^3-4x^2y^2+4xy\right)+\left(2x^2y^2-4xy+4\right)\)
\(=x^2y^2\left(x^2y^2-2xy+2\right)+2xy\left(x^2y^2-2xy+2\right)+2\left(x^2y^2-2xy+2\right)\)
= (x2y2 + 2xy + 2)(x2y2 - 2xy + 2)
\(x^4+4=x^4+4+4x^2-4x^2\)
\(=\left(x^4+4x^2+4\right)-\left(2x\right)^2\)
\(=\left(x^2+2\right)^2-\left(2x\right)^2=\left(x^2-2x+2\right)\left(x^2+2x+2\right)\)
\(x^8+3x^4+4\)
\(=x^8+x^6+2x^4-x^6-x^4-2x^2+2x^4+2x^2+4\)
\(=\left(x^8+x^6+2x^4\right)-\left(x^6+x^4+2x^2\right)+\left(2x^4+2x^2+4\right)\)
\(=x^4\left(x^4+x^2+2\right)-x^2\left(x^4+x^2+2\right)+2\left(x^4+x^2+2\right)\)
\(=\left(x^4-x^2+2\right)\left(x^4+x^2+2\right)\)
Ta có : \(x^4+4\)
\(=x^4+4x^2+4-4x^2\)
\(=\left(x^2+2\right)^2-4x^2\)
\(=\left(x^2+2-2x\right)\left(x^2+2+2x\right)\)
\(x^4+4=\left(x^4+4x^2+4\right)-4x^2=\left(x^2+2\right)^2-\left(2x\right)^2=\left(x^2+2x+2\right)\left(x^2-2x+2\right)\)