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#)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:
\(x^3-2x-4\)
\(=x^3-2x^2+2x^2-4x+2x-4\)
\(=x^2\left(x-2\right)+2x\left(x-2\right)+2\left(x-2\right)\)
\(=\left(x-2\right)\left(x^2+2x+2\right)\)
\(x^4.y^4+4\)
\(=\left(x^4y^4-2x^3y^3+2x^2y^2\right)+\left(2x^3y^3-4x^2y^2+4xy\right)+\left(2x^2y^2-4xy+4\right)\)
\(=x^2y^2\left(x^2y^2-2xy+2\right)+2xy\left(x^2y^2-2xy+2\right)+2\left(x^2y^2-2xy+2\right)\)
= (x2y2 + 2xy + 2)(x2y2 - 2xy + 2)
Có: \(\left(x+y\right)^4+x^4+y^4\)
\(=\left(x+y\right)^4+\left(x^2+y^2\right)^2-2x^2y^2\)
\(=\left[\left(x+y\right)^4-x^2y^2\right]+\left[\left(x^2+y^2\right)^2-x^2y^2\right]\)
\(=\left[\left(x^2+y^2+2xy\right)^2-\left(xy\right)^2\right]+\left[\left(x^2+y^2\right)^2-\left(xy\right)^2\right]\)
\(=\left(x^2+y^2+xy\right)\left(x^2+y^2+3xy\right)+\left(x^2+y^2+xy\right)\left(x^2+y^2-xy\right)\)
\(=2\left(x^2+y^2+xy\right)\left(x^2+y^2+xy\right)=2\left(x^2+y^2+xy\right)^2\)
x4y4+64=x4y4+16x2y2+64-16x2y2
=(x2y2+8)2-16x2y2
=(x2y2-4xy+8)(x2y2+4xy+8)
Ta có: \(x^4+6^4=x^4+72x^2+6^4-72x^2\)
\(=\left(x^2+36\right)-72x^2\)
\(=\left(x^2+36-\sqrt{72}x\right)\left(x^2+36+\sqrt{72}x\right)\)
x^4+x^2+1 = (x^4+2x^2+1)-x^2 = (x^2+1)^2-x^2 = (x^2-x+1).(x^2+x+1)
k mk nha
x5-x4-1=x5-x3-x2-x4+x2+x+x3-x-1
=x2.(x3-x-1)-x.(x3-x-1)+(x3-x-1)
=(x3-x-1)(x2-x+1)
x^4+x^2+1 = (x^4+2x^2+1)-x^2 = (x^2+1)^2-x^2 = (x^2-x+1).(x^2+x+1)
k mk nha
x4+4
=x4+4x2+4-4x2
=(x4+4x2+4)-(2x)2
=(x2+2)2-(2x)2
= (x2+2x+2).(x2-2x+2)
x^4 + 4
=x^4 + 4 + 4x^2 - 4x^2
=(x^4 + 4x^2 +4 ) - 4x^2
=(x^2+4)^2 -(2x)^2
=(x^2+4+2x)(x^2+4-2x)