phân tích đa thức thành nhân tử
a) 2x8-12x4+18
b) a4b+6a2b3+9b5
c) -2a6-8a3b-8b2
d) 4x+4xy6+xy12
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a, \(x^2\) + 4\(x\) - y2 + 4
= (\(x^2\) + 4\(x\) + 4) - y2
= (\(x\) + 2)2 - y2
= (\(x\) + 2 - y)(\(x\) + 2 + y)
b, 2\(x^2\) - 18
= 2.(\(x^2\) -9)
= 2.(\(x\) -3).(\(x\) + 3)
\(2a^2+8b^2-8ab\)
\(=2\left(a^2-4ab+4b^2\right)\)
\(=2\left(a-2b\right)^2\)
a) `64-96a+48a^2-8a^3`
`=-(8a^3-48a^2+96a-64)`
`=-[(2a)^3 - 3.(2a)^2 .4 + 3.2a.4^2 - 4^3]`
`=-(2a-4)^3`
b) `-m^3n^6-8`
`=-(m^3n^6+8)`
`=-[(mn^2)^3+2^3]`
`=-(mn^2+2)(m^2n^4-2mn^2+4)`.
Phân tích đa thức thành nhân tử(tách hạng tử)
1)x^2+2x-3=x^2-x+3x-3=x(x-1)+3(x-1)=(x-1)(x+3)
2)x^2-5x+6=x^2-2x-3x+6=x(x-2)-3(x-2)=(x-2)(x-3)
3)x^2+7x+12=(x+3)(x+4)
4)x^2-x-12=(x-4)(x+3)
5)3x^2+3x-36=3[(x-3)(x+4)]
6)5x^2-5x-10=5[(x-2)(x+1) ]
7)3x^2-7x-6=(x-3)(3x+2)
8)4x^2+4x-3=4x^2+6x-2x-3=(2x-1)(2x+3)
9)8x^2-2x-3=8x^2+4x-6x-3=(4x-3)(2x+1)
1: \(x^2+2x-3=\left(x+3\right)\left(x-1\right)\)
2: \(x^2-5x+6=\left(x-2\right)\left(x-3\right)\)
3: \(x^2+7x^2+12x=4x\left(2x+3\right)\)
4: \(x^2-x-12=\left(x-4\right)\left(x+3\right)\)
5: \(3x^2+3x-36=3\left(x^2+x-12\right)=3\left(x+4\right)\left(x-3\right)\)
6: \(5x^2-5x-10=5\left(x^2-x-2\right)=5\left(x-2\right)\left(x+1\right)\)
a) 4x2 + 4x - 3x = 4x2 +x = x( 4x+1)
b) x2+7x+10= x2+2x+5x+10= x(x+2)+5(x+2)= (x+5)(x+2)
c) x2-x-12= x2 - 4x+3x-12= x(x-4)+3(x-4)=(x+3)(x-4)
d) x2+3x-18=x2+6x-3x-18= x(x+6)-3(x+6)=(x-3)(x+6)
Bài này sử dụng \(a^2-b^2=\left(a-b\right)\left(a+b\right).\)
a) \(4b^2c^2-\left(b^2+c^2-a^2\right)^2=\left(2bc-b^2-c^2+a^2\right)\left(2bc+b^2+c^2-a^2\right)\)
\(=\left(a^2-\left(b-c\right)^2\right)\left(\left(b+c\right)^2-a^2\right)=\left(a-b+c\right)\left(a+b-c\right)\left(a+b+c\right)\left(b+c-a\right)\)
b) \(\left(4x^2-3x-18\right)^2-\left(4x^2+3x\right)^2=\left(4x^2-3x-18-4x^2-3x\right)\left(4x^2-3x-18+4x^2+3x\right)\)
\(=\left(-6x-18\right)\left(8x^2-18\right)=-12\left(x+3\right)\left(4x^2-9\right)=-12\left(x+3\right)\left(2x-3\right)\left(2x+3\right).\)
c) \(\left(4abcd+\left(a^2+b^2\right)\left(c^2+d^2\right)\right)^2-4\left(cd\left(a^2+b^2\right)+ab\left(c^2+d^2\right)\right)^2\)
\(=\left(4abcd+\left(a^2+b^2\right)\left(c^2+d^2\right)-2cd\left(a^2+b^2\right)-2ab\left(c^2+d^2\right)\right)\times\)
\(\times\left(4abcd+\left(a^2+b^2\right)\left(c^2+d^2\right)+2cd\left(a^2+b^2\right)+2ab\left(c^2+d^2\right)\right)\)
\(=\left(\left(a^2+b^2\right)\left(c-d\right)^2-2ab\left(c-d\right)^2\right)\times\left(\left(a^2+b^2\right)\left(c+d\right)^2+2ab\left(c+d\right)^2\right)\)
\(=\left(c-d\right)^2\cdot\left(a-b\right)^2\cdot\left(a+b\right)^2\cdot\left(c+d\right)^2.\)
a) Ta có: \(\left(4x^2-3x-18\right)^2-\left(4x^2+3x\right)^2\)
\(=\left(4x^2-3x-18-4x^2-3x\right)\left(4x^2-3x-18+4x^2+3x\right)\)
\(=\left(-6x-18\right)\left(8x^2-18\right)\)
\(=-6\left(x+3\right)\cdot2\left(4x^2-9\right)\)
\(=-12\left(x+3\right)\left(2x-3\right)\left(2x+3\right)\)
b) Ta có: \(9\left(x+y-1\right)^2-4\left(2x+3y+1\right)^2\)
\(=\left(3x+3y-3\right)^2-\left(4x+6y+2\right)^2\)
\(=\left(3x+3y-3-4x-6y-2\right)\left(3x+3y-3+4x+6y+2\right)\)
\(=-\left(x+3y+5\right)\left(7x+9y-1\right)\)
c) Ta có: \(-4x^2+12xy-9y^2+25\)
\(=-\left(4x^2-12xy+9y^2-25\right)\)
\(=-\left[\left(2x-3y\right)^2-25\right]\)
\(=-\left(2x-3y-5\right)\left(2x-3y+5\right)\)
d) Ta có: \(x^2-2xy+y^2-4m^2+4mn-n^2\)
\(=\left(x^2-2xy+y^2\right)-\left(4m^2-4mn+n^2\right)\)
\(=\left(x-y\right)^2-\left(2m-n\right)^2\)
\(=\left(x-y-2m+n\right)\left(x-y+2m-n\right)\)
Bài làm
a) x4+x3+2x2+x+1=(x4+x3+x2)+(x2+x+1)=x2(x2+x+1)+(x2+x+1)=(x2+x+1)(x2+1)
b)a3+b3+c3-3abc=a3+3ab(a+b)+b3+c3 -(3ab(a+b)+3abc)=(a+b)3+c3-3ab(a+b+c)
=(a+b+c)((a+b)2-(a+b)c+c2)-3ab(a+b+c)=(a+b+c)(a2+2ab+b2-ac-ab+c2-3ab)=(a+b+c)(a2+b2+c2-ab-ac-bc)
c)Đặt x-y=a;y-z=b;z-x=c
a+b+c=x-y-z+z-x=o
đưa về như bài b
d)nhóm 2 hạng tử đầu lại và 2hangj tử sau lại để 2 hạng tử sau ở trong ngoặc sau đó áp dụng hằng đẳng thức dề tính sau đó dặt nhân tử chung
e)x2(y-z)+y2(z-x)+z2(x-y)=x2(y-z)-y2((y-z)+(x-y))+z2(x-y)
=x2(y-z)-y2(y-z)-y2(x-y)+z2(x-y)=(y-z)(x2-y2)-(x-y)(y2-z2)=(y-z)(x2-2y2+xy+xz+yz)
a/ \(=2\left(x^8-6x^4+9\right)=2\left(x^4-3\right)^2\)
b/ \(=b\left(a^4+6a^2b^2+9b^4\right)=b\left(a^2+3b^2\right)^2\)
c/ \(=-2\left(a^6+4a^3b+4b^2\right)=-2\left(a^3+2b\right)^2\)
d/ \(=x\left(y^{12}+4y^6+4\right)=x\left(y^6+2\right)^2\)