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a ) \(2x^4-9x^3+4x^2+21x-18\)
\(=2x^4-2x^3-7x^3+7x^2-3x^2+3x+18x-18\)
\(=2x^3\left(x-1\right)-7x^2\left(x-1\right)-3x\left(x-1\right)+18\left(x-1\right)\)
\(=\left(2x^3-7x^2-3x+18\right)\left(x-1\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(3x^4+2x^3-8x^2-2x+5\)
\(=3x^4-3x^3+5x^3-5x^2-3x^2+3x-5x+5\)
\(=3x^3\left(x-1\right)+5x^2\left(x-1\right)-3x\left(x-1\right)-5\left(x-1\right)\)
\(=\left(3x^3+5x^2-3x-5\right)\left(x-1\right)\)
\(=\left[3x\left(x^2-1\right)+5\left(x^2-1\right)\right]\left(x-1\right)\)
\(=\left(3x+5\right)\left(x^2-1\right)\left(x-1\right)\)
\(=\left(3x+5\right)\left(x+1\right)\left(x-1\right)\left(x-1\right)=\left(3x+5\right)\left(x+1\right)\left(x-1\right)^2\)
b, \(2x^4-9x^3+4x^2+21x-18\)
\(=2x^4-2x^3-7x^3+7x^2-3x^2+3x+18x-18\)
\(=2x^3\left(x-1\right)-7x^2\left(x-1\right)-3x\left(x-1\right)+18\left(x-1\right)\)
\(=\left(2x^3-7x^2-3x+18\right)\left(x-1\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(B=\left(x^2+2x\right)-2x^2-4x-3\)
\(=\left(x^2+2x\right)^2-2\left(x^2+2x\right)-3\) \(\left(1\right)\)
Đặt \(x^2+2x=t\) , khi đó \(\left(1\right)\Leftrightarrow t^2-2t-3=\left(t+1\right)\left(t-3\right)=\left(x^2+2x+1\right)\left(x^2+2x-3\right)=\left(x+1\right)^2\left(x-1\right)\left(x+3\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
4x4 + 4x3 + 5x2 + 2x +1
= (4x4 + 4x3 + x2 ) + ( 2x2 + 1 ) + 1
= x2(2x + 1 )2 + 2x(2x + 1) +1
= (x(2x + 1 ) + 1)2
= (2x + x + 1)2
![](https://rs.olm.vn/images/avt/0.png?1311)
4x4+4x3+5x2+2x+1
=(4x4+4x3+x2) + (2x2+1) +1
= x2(2x+1)2 + 2x(2x+1) +1
= (x(2x+1)+1)2
=(2x2+x+1)2
![](https://rs.olm.vn/images/avt/0.png?1311)