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Bài 1 :
\(x^2-6x+8=x^2-2x-4x+8=x\left(x-2\right)-4\left(x-2\right)=\left(x-4\right)\left(x-2\right)\)
Bài 2 :
\(x^8+x^7+1=x^8+x^7+x^6+x^5+x^4+x^3+x^2+x+1-x^6-x^5-x^4-x^3-x^2-x\)
\(=x^6\left(x^2+x+1\right)+x^3\left(x^2+x+1\right)+x^2+x+1-x^4\left(x^2+x+1\right)-x\left(x^2+x+1\right)\)
=\(\left(x^2+x+1\right)\left(x^6+x^3+1-x^4-x\right)\)
Tick đúng nha
![](https://rs.olm.vn/images/avt/0.png?1311)
\(A=\left(x-1\right)\left(x-2\right)\left(x+7\right)\left(x+8\right)+8\)
\(A=\left[\left(x-1\right)\left(x+7\right)\right]\left[\left(x-2\right)\left(x+8\right)\right]+8\)
\(A=\left(x^2+6x-7\right)\left(x^2+6x-16\right)+8\)
Đặt \(q=x^2+6x-7\)ta có :
\(A=q\left(q-9\right)+8\)
\(A=q^2-9q+8\)
\(A=q^2-q-8q+8\)
\(A=q\left(q-1\right)-8\left(q-1\right)\)
\(A=\left(q-1\right)\left(q-8\right)\)
Thay \(q=x^2+6x-7\)vào A ta được :
\(A=\left(x^2+6x-7-1\right)\left(x^2+6x-7-8\right)\)
\(A=\left(x^2+6x-8\right)\left(x^2+6x-15\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(x^3-\left(\frac{1}{2}\right)^3\)
\(=\left(x-\frac{1}{2}\right)\left(x^2+x.\frac{1}{2}+\left(\frac{1}{2}\right)^2\right)\)
\(=\left(x-\frac{1}{2}\right)\left(x^2+\frac{1}{2}x+\frac{1}{4}\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
x8+x+1 = x8- x2 + x2 x+1 = x2(x6-1) + (x2+x+1)
= x2(x3-1) (x3+1)+ (x2+x+1)
= x2(x-1)(x2+x+1) (x3+1)+ (x2+x+1)
= (x2+x+1)[ x2(x-1) (x3+1)+1)
= ....
trong ngoặc vuông bạn làm tiếp nhé. nhớ tick cho mình
![](https://rs.olm.vn/images/avt/0.png?1311)
\(x^8+x+1\)
\(=x^8-x^7+x^5-x^4+x^2+x^7-x^6+x^4-x^3+x+x^6-x^5+x^3-x^2+1\)
\(=\left(x^8-x^7+x^5-x^4+x^2\right)+\left(x^7-x^6+x^4-x^3+x\right)+\left(x^6-x^5+x^3-x^2+1\right)\)
\(=x^2\left(x^6-x^5+x^3-x^2+1\right)+x\left(x^6-x^5+x^3-x^2+1\right)+\left(x^6-x^5+x^3-x^2+1\right)\)
\(=\left(x^6-x^5+x^3-x^2+1\right)\left(x^2+x+1\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
đề sai nha bạn
mình sửa đề cho:
\(A=\left(x+1\right)\left(x+2\right)\left(x+7\right)\left(x+8\right)+8\)
\(A=\left(x+1\right)\left(x+8\right)\left(x+2\right)\left(x+7\right)+8\)
\(A=\left(x^2+9x+8\right)\left(x^2+9x+14\right)+8\)
Đặt \(x^2+9x+8=a\)
\(\Rightarrow A=a\left(a+6\right)+8=a^2+6a+8=\left(a+2\right)\left(a+4\right)\)
\(\Rightarrow A=\left(x^2+9x+8+2\right)\left(x^2+9x+8+4\right)=\left(x^2+9x+10\right)\left(x^2+9x+12\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a,x8+x+1
=x8+x2+x+1-x2
=x2(x6-1)+(x2+x+1)
=x2(x3-1)(x3+1)+(x2+x+1)
=x2(x-1)(x2+x+1)(x3+1)+(x2+x+1)
=(x2+x+1)[x2(x-1)(x3+1)+1]
=(x2+x+1)(x6+x3-x^5-x2+1)
b,x8+x7+1
=x8+x7+x2+x+1-x2-x
=x2(x6-1)+x(x6-1)+(x2+x+1)
=x2(x-1)(x2+x+1)(x3+1)+x(x-1)(x2+x+1)(x3+1)+(x2+x+1)
=(x2+x+1)[x2(x-1)(x3+1)+x(x-1)(x3+1)+1)]
=(x2+x+1)(x6-x4+x3-x+1)