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\(x^5+x+1=x^5+x^4-x^4+x^3-x^3+x^2-x^2+x+1\)
\(=\left(x^5+x^4+x^3\right)+\left(x^2+x+1\right)-\left(x^4+x^3+x^2\right)\)
\(=x^3\left(x^2+x+1\right)+\left(x^2+x+1\right)-x^2\left(x^2+x+1\right)\)
\(=\left(x^2+x+1\right)\left(x^3-x^2+1\right)\)
\(x^{10}+x^5+1\)
\(=\left(x^{10}-x^9+x^7-x^6+x^5-x^3+x^2\right)\)
\(+\left(x^9-x^8+x^6-x^5+x^4-x^2+x\right)\)
\(+\left(x^8-x^7+x^5-x^4+x^3-x+1\right)\)
\(=x^2\left(x^8-x^7+x^5-x^4+x^3-x+1\right)\)
\(+x\left(x^8-x^7+x^5-x^4+x^3-x+1\right)\)
\(+\left(x^8-x^7+x^5-x^4+x^3-x+1\right)\)
\(=\left(x^2+x+1\right)\left(x^8-x^7+x^5-x^4+x^3-x+1\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a)\(x^2+9x+20\)
\(\Leftrightarrow x^2+4x+5x+20\)
\(\Leftrightarrow x\left(x+4\right)+5\left(x+4\right)\)
\(\Leftrightarrow\left(x+5\right)\left(x+4\right)\)
b)\(x^2+x-12\)
\(\Leftrightarrow x-3x+4x-12\)
\(\Leftrightarrow x\left(x-3\right)+4\left(x-3\right)\)
\(\Leftrightarrow\left(x+4\right)\left(x-3\right)\)
Vừa vừa phải phải thôi người ta mất công gửi lên còn chửi người ta đó điên mất lịch sự
![](https://rs.olm.vn/images/avt/0.png?1311)
Đa thức có dạng \(x^{3a+1}+x^{3b+2}+1\) thì đưa về dạng \(\left(x^2+x+1\right)\cdot P\left(x\right)\) bạn nhé!
Bài làm:
\(x^5+x+1\)
\(=\left(x^5-x^2\right)+\left(x^2+x+1\right)\)
\(=x^2\left(x^3-1^3\right)+\left(x^2+x+1\right)\)
\(=x^2\left(x-1\right)\left(x^2+x+1\right)+\left(x^2+x+1\right)\)
\(=\left(x^2+x+1\right)\left(x^3-x^2+1\right)\)
\(x^5+x+1=x^5-x^2+x^2+x+1\)
\(=x^2\left(x^3-1\right)+x^2+x+1\)
\(=x^2\left(x-1\right)\left(x^2+x+1\right)+\left(x^2+x+1\right)\)
\(=\left(x^2+x+1\right)\left(x^2\left(x-1\right)+1\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có:
\(x^5+x-1=\left(x^5+x^2\right)-\left(x^2-x+1\right)=x^2\left(x+1\right)\left(x^2-x+1\right)-\left(x^2-x+1\right)\)
\(=\left(x^2-x+1\right)\left(x^3+x^2-1\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
x5 + x4 + 1 = x5 - x3 - x2 - x4 + x2 + x + x3 - x - 1
= x2 ( x3 - x - 1 ) - x ( x3 - x - 1 ) + 1 ( x3 - x - 1 )
= ( x3 - x - 1 ) ( x2 - x + 1 )
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\(x^7+x^2+1\)
\(=x^7+x^6+x^5+x^4+x^3+x^2+x+1\)
\(=x^5\left(x^2+x+1\right)-x^4\left(x^2+x+1\right)+x^2\left(x^2+x+1\right)-x\left(x^2+x+1\right)+\left(x^2+x+1\right)\)
\(=\left(x^2+x+1\right)\left(x^5-x^4+x^2-x+1\right)\)
a) \(x^7+x^2+1=\left(x^7-x\right)+\left(x^2+x+1\right)\)
\(=x\left(x^6-1\right)+\left(x^2+x+1\right)=x\left(x^3-1\right)\left(x^3+1\right)+\left(x^2+x+1\right)\)
\(=x\left(x-1\right)\left(x^2+x+1\right)\left(x^3+1\right)+\left(x^2+x+1\right)\)
\(=\left(x^2+x+1\right)\left[x\left(x-1\right)\left(x^3+1\right)+1\right]\)
\(=\left(x^2+x+1\right)\left(x^5-x^4+x^2-x+1\right)\)
b) \(x^7+x^5+1=\left(x^7+x^6+x^5\right)-\left(x^6-1\right)\)
\(=x^5\left(x^2+x+1\right)-\left(x^3-1\right)\left(x^3+1\right)\)
\(=x^5\left(x^2+x+1\right)-\left(x-1\right)\left(x^2+x+1\right)\left(x^3+1\right)\)
\(=\left(x^2+x+1\right)\left[x^5-\left(x-1\right)\left(x^3+1\right)\right]\)
\(=\left(x^2+x+1\right)\left(x^5-x^4+x^3-x+1\right)\)
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mình chỉ phân tích được đa thức này thôi!
\(x^4+x^2+1\)
\(=x^4+2x^2-x^2+1\)
\(=\left(x^4+2x^2+1\right)-x^2\)
\(=\left(x^2+1\right)^2-x^2\)
\(=\left(x^2+x+1\right)\left(x^2-x+1\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(x^8+x^4+1\)
\(=x^8+x^7+x^6-x^7-x^6-x^5+x^5+x^4+x^3-x^3-x^2-x+x^2+x+1\)
\(=\left(x^8+x^7+x^6\right)-\left(x^7+x^6+x^5\right)+\left(x^5+x^4+x^3\right)-\left(x^3+x^2+x\right)+\left(x^2+x+1\right)\)
\(=x^6\left(x^2+x+1\right)-x^5\left(x^2+x+1\right)+x^3\left(x^2+x+1\right)-x\left(x^2+x+1\right)+\left(x^2+x+1\right)\)
\(=\left(x^2+x+1\right)\left(x^6-x^5+x^3-x+1\right)\)
\(x^5-x^4-1\)
\(=x^5-x^4+x^3-x^3+x^2-x-x^2+x-1\)
\(=\left(x^5-x^4+x^3\right)-\left(x^3-x^2+x\right)-\left(x^2-x+1\right)\)
\(=x^3\left(x^2-x+1\right)-x\left(x^2-x+1\right)-\left(x^2-x+1\right)\)
\(=\left(x^2-x+1\right)\left(x^3-x-1\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có:
\(x^7+x^5+1=x.x.x.x.x.x.x+x.x.x.x.x+1\)
\(=x.x.x.x.x\left(x.x+1\right)\)
Kết quả như vậy phải không. Mình chưa học mới xem sơ thôi. Nếu sai bạn đừng trách.
Sau khi phân tích thì đa thức có dạng ( x2 + ax + 1 )( x3 + bx2 + cx + 1 )
=> x5 + x + 1 = ( x2 + ax + 1 )( x3 + bx2 + cx + 1 )
=> x5 + x + 1 = x5 + bx4 + cx3 + x2 + ax4 + abx3 + acx2 + ax + x3 + bx2 + cx + 1
=> x5 + x + 1 = x5 + ( a + b )x4 + ( ab + c + 1 )x3 + ( ac + b + 1 )x2 + ( c + a )x + 1
Đồng nhất hệ số ta có :
a + b = 0 ; ab + c + 1 = 0 ; ac + b + 1 = 0 ; c + a = 1
Giải hệ này ta được : a = 1 ; b = -1 ; c = 0
=> x5 + x + 1 = ( x2 + x + 1 )( x3 - x2 + 1 )
\(x^5+x+1=\left(x^5-x^2\right)+\left(x+x^2+1\right)=x^2\left(x^3-1\right)+\left(x^2+x+1\right)=x^2\left(x-1\right)\left(x^2+x+1\right)\)
\(+\left(x^2+x+1\right)=\left(x^2+x+1\right)\left(x^3-x^2+1\right)\)