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\(2x^2-x^2-3x-1\)
\(=x^2-3x-1\)
\(=\frac{1}{4}\left(4x^2-12x-4\right)\)
\(=\frac{-1}{4}\left[13-\left(4x-12x+9\right)\right]\)
\(=-\frac{1}{4}\left[13-\left(2x-3\right)^2\right]\)
\(=-\frac{1}{4}\left(\sqrt{13}-2x+3\right)\left(\sqrt{13}+2x-3\right)\)
\(x^7+x^2+1\)
\(=x^7+x^6+x^5+x^4+x^3+x^2+x+1\)
\(=x^5\left(x^2+x+1\right)-x^4\left(x^2+x+1\right)+x^2\left(x^2+x+1\right)-x\left(x^2+x+1\right)+\left(x^2+x+1\right)\)
\(=\left(x^2+x+1\right)\left(x^5-x^4+x^2-x+1\right)\)
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) \(x^7+x^5+1=\left(x^7+x^6+x^5\right)-\left(x^6-1\right)\)
\(=x^5\left(x^2+x+1\right)-\left(x^3-1\right)\left(x^3+1\right)\)
\(=x^5\left(x^2+x+1\right)-\left(x-1\right)\left(x^2+x+1\right)\left(x^3+1\right)\)
\(=\left(x^2+x+1\right)\left[x^5-\left(x-1\right)\left(x^3+1\right)\right]\)
\(=\left(x^2+x+1\right)\left(x^5-x^4+x^3-x+1\right)\)
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.
\(x^{11}+x^7+1=x^{11}+x^7+x^4+1-x^4\)
\(=x^7\left(x^4+1\right)+\left(x^4+1\right)-x^4=\left(x^4+1\right)\left(x^7+1\right)-x^4\)
\(=\left(\sqrt{\left(x^4+1\right)\left(x^7+1\right)}+x^2\right)\left(\sqrt{\left(x^4+1\right)\left(x^7+1\right)}-x^2\right)\)
\(x^5+x+1=x^5+x^4-x^4+x^3-x^3+x^2-x^2+x+1\)
\(=\left(x^5+x^4+x^3\right)+\left(x^2+x+1\right)-\left(x^4+x^3+x^2\right)\)
\(=x^3\left(x^2+x+1\right)+\left(x^2+x+1\right)-x^2\left(x^2+x+1\right)\)
\(=\left(x^2+x+1\right)\left(x^3-x^2+1\right)\)
\(x^{10}+x^5+1\)
\(=\left(x^{10}-x^9+x^7-x^6+x^5-x^3+x^2\right)\)
\(+\left(x^9-x^8+x^6-x^5+x^4-x^2+x\right)\)
\(+\left(x^8-x^7+x^5-x^4+x^3-x+1\right)\)
\(=x^2\left(x^8-x^7+x^5-x^4+x^3-x+1\right)\)
\(+x\left(x^8-x^7+x^5-x^4+x^3-x+1\right)\)
\(+\left(x^8-x^7+x^5-x^4+x^3-x+1\right)\)
\(=\left(x^2+x+1\right)\left(x^8-x^7+x^5-x^4+x^3-x+1\right)\)
Ta có:
\(x^9-x^7-x^6-x^5+x^4+x^3+x^2-1\)
\(=\left(x^9-x^8\right)+\left(x^8-x^7\right)-\left(x^6-x^5\right)-\left(2x^5-2x^4\right)-\left(x^4-x^3\right)+\left(x^2-x\right)+\left(x-1\right) \)
\(=x^8.\left(x-1\right)+x^7.\left(x-1\right)-x^5.\left(x-1\right)-2x^4.\left(x-1\right)-x^3\left(x-1\right)+x\left(x-1\right)+\left(x-1\right)\)
\(=\left(x-1\right)\left(x^8+x^7-x^5-2x^4-x^3+x+1\right)\)
Ta có: x^7 + x^5 + 1 = x^7 - x + x^5 - x^2 + x^2 + x + 1
=x(x^6 - 1) + x^2(x^3 - 1) + (x^2 +x +1)
=x(x^3 -1)(x^3 +1) +x^2(x^3-1) + (x^2 + x + 1)
=x(x-1)(x^2 + x +1)(x^3 +1) + x^2(x-1)(x^2 +x +1) +(x^2 +x +1)
=(x^2 +x +1)[x(x-1)(x^3 +1) +x^2(x-1) +1]
=(x^2 +x +1)[ x^5 - x^4 + x^3 - x + 1]
\(x^7+x^5-1\)
\(=x^7+x^6+x^5-x^3-x^2-x^6-x^5-x^4+x^2+x+x^5+x^4+x^3-x-1\)
\(=x^2\left(x^5+x^4+x^3-x-1\right)-x\left(x^5+x^4+x^3-x-1\right)+\left(x^5+x^4+x^3-x-1\right)\)
\(=\left(x^2-x+1\right)\left(x^5+x^4+x^3-x-1\right)\)
\(=x^7-x+x^5+x^2-\left(x^2-x+1\right)=x\left(x^3-1\right)\left(x^3+1\right)+x^2\left(x^3+1\right)-\left(x^2-x+1\right)\)\(=x\left(x^3-1\right)\left(x+1\right)\left(x^2-x+1\right)+x^2\left(x+1\right)\left(x^2-x+1\right)-\left(x^2-x+1\right)\)
Tự Tính Tiếp!!!!!!!!!