Phân tích nhân tử
x(x-4)(x-1)(x+3)+36
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\(x^3\left(2+x\right)^2-\left(x+2\right)^2+1-x^3\\ =\left(x+2\right)^2\left(x^3-1\right)-\left(x^3-1\right)\\ =\left[\left(x+2\right)^2-1\right]\left(x^3-1\right)\\ =\left(x-1\right)\left(x^2+x+1\right)\left(x^2+4x+3\right)=\left(x-1\right)\left(x+1\right)\left(x+3\right)\left(x^2+x+1\right)\)
\(=x^2\left(x+y\right)-\left(x+y\right)=\left(x^2-1\right)\left(x+y\right)=\left(x-1\right)\left(x+1\right)\left(x+y\right)\)
\(x^4+x^3+2x^2+x+1=\left(x^4+x^3+x^2\right)+\left(x^2+x+1\right)\\ =x^2\left(x^2+x+1\right)+\left(x^2+x+1\right)=\left(x^2+1\right)\left(x^2+x+1\right)\)
Dễ thấy \(x^2+1>0\); \(x^2+x+1=\left(x+\dfrac{1}{2}\right)^2+\dfrac{3}{4}>0\) nên ta không thể phân tích thêm được nữa.
Vậy \(x^4+x^3+2x^2+x+1=\left(x^2+1\right)\left(x^2+x+1\right)\).
\(x^5+x+1\)
\(=x^5+x^4+x^3-x^4-x^3-x^2+x^2+x+1\)
\(=\left(x^2+x+1\right)\left(x^3-x^2+1\right)\)
\(x^2\left(x-3\right)-4x+12=\left(x-3\right)\left(x-2\right)\left(x+2\right)\)
=x²(x-3)-4x+3.4
=x²(x-3)-4(x+3)
=x²(x-3)+4(x-3)
=(x-3)(x²+4)
=(x-3)(x²+2²)
=(x-3)(x-2)(x+2)
Câu 1:
\(=x^2-\left(y-4\right)^2\)
\(=\left(x-y+4\right)\cdot\left(x+y-4\right)\)
\(x^3-2xy-x^2y+2y^2=\left(x^3-x^2y\right)-\left(2xy-2y^2\right)\)
\(=x^2\left(x-y\right)-2y\left(x-y\right)=\left(x^2-2y\right)\left(x-y\right)\)
\(=x^2\left(x-y\right)-2y\left(x-y\right)\)
\(=\left(x-y\right)\left(x^2-2y\right)\)
x(x-4)(x-1)(x+3)+36=[x(x-1)][(x-4)(x+3)]+36
\(=\left(x^2-x\right)\left(x^2-x-12\right)+36\)
Đặt \(t=x^2-x-6\)ta có:
(t+6)(t-6)+36
=t^2 -36 +36
=t^2=....
\(x\left(x-4\right)\left(x-1\right)\left(x+3\right)+36\)
\(=x^4-2x^3-11x^2+12x+36\)
\(=x^4-\left(6x^3-4x^2\right)+\left(9x^2-24x^2+4x^2\right)+\left(36x-24x\right)+36\)
\(=x^4-6x^3+9x^2+4x^3-24x^2+36x+4x^2-24x+36\)
\(=x^2\left(x^2-6x+9\right)+4x\left(x^2-6x+9\right)+4\left(x^2-6x+9\right)\)
\(=\left(x^2-6x+9\right)\left(x^2+4x+4\right)\)
\(=\left(x-3\right)^2\left(x+2\right)^2\)
Xong!