1.phân tích đa thức thành nhân tử:
a.4x^2-4x+15
b.x^2+3xy+y^2
c.x^4-3x^2+9
d.x^4+x^2+1
e.-c^2(a-b)+2^2(a-c)-a^2(b-c)
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a.
\(=\left(x+1\right)^3-\left(3z\right)^3\)
\(=\left(x+1+3z\right)\left[\left(x+1\right)^2+3z\left(x+1\right)+9z^2\right]\)
\(=\left(x+3z+1\right)\left(x^2+2x+1+3zx+3z+9z^2\right)\)
b.
\(=\left(x-y\right)^2-z\left(x-y\right)\)
\(=\left(x-y\right)\left(x-y-z\right)\)
c.
\(=x^4-1+4x^2-4\)
\(=\left(x^2-1\right)\left(x^2+1\right)+4\left(x^2-1\right)\)
\(=\left(x^2-1\right)\left(x^2+5\right)\)
\(=\left(x-1\right)\left(x+1\right)\left(x^2+5\right)\)
a) Ta có: \(x^3+3x^2+3x+1-27z^3\)
\(=\left(x+1\right)^3-\left(3z\right)^3\)
\(=\left(x+1-3z\right)\left(x^2+2x+1+3xz+3z+9z^2\right)\)
b) Ta có: \(x^2-2xy+y^2-zx+yz\)
\(=\left(x-y\right)^2-z\left(x-y\right)\)
\(=\left(x-y\right)\left(x-y-z\right)\)
c) Ta có: \(x^4+4x^2-5\)
\(=x^4+4x^2+4-9\)
\(=\left(x^2+2\right)^2-3^2\)
\(=\left(x^2-1\right)\left(x^2+5\right)\)
\(=\left(x-1\right)\left(x+1\right)\left(x^2+5\right)\)
Lời giải:
a.
$ab(a-b)+bc(b-c)+ca(c-a)$
$=ab(a-b)-bc[(a-b)+(c-a)]+ca(c-a)$
$=ab(a-b)-bc(a-b)-bc(c-a)+ca(c-a)$
$=(a-b)(ab-bc)-(c-a)(bc-ca)=b(a-b)(a-c)-c(c-a)(b-a)$
$=b(a-b)(a-c)-c(a-c)(a-b)=(a-b)(b-c)(a-c)$
b.
$x^2-3xy-10y^2=(x^2+2xy)-(5xy+10y^2)$
$=x(x+2y)-5y(x+2y)=(x+2y)(x-5y)$
c.
$3x(x-2)-x+2=3x(x-2)-(x-2)=(x-2)(3x-1)$
\(a,ab\left(a-b\right)+bc\left(b-c\right)+ca\left(c-a\right)\\ =a^2b-ab^2+b^2c-bc^2+ca\left(c-a\right)\\ =\left(a^2b-bc^2\right)-\left(ab^2-b^2c\right)+ca\left(c-a\right)\\ =b\left(a-c\right)\left(a+c\right)-b^2\left(a-c\right)-ca\left(a-c\right)\\ =\left(a-c\right)\left(ab+bc-b^2-ca\right)\\ =\left(a-c\right)\left(b-c\right)\left(a-b\right)\)
\(b,x^2-3xy-10y^2\\ =x^2+2xy-5xy-10y^2\\ =x\left(x+2y\right)-5y\left(x+2y\right)=\left(x-5y\right)\left(x+2y\right)\)
\(c,3x\left(x-2\right)-x+2=3x\left(x-2\right)-\left(x-2\right)=\left(3x-1\right)\left(x-2\right)\)
\(A=x^2+3x+2=\left(x+1\right)\left(x+2\right)\)
\(B=x^2-4x-5=\left(x-5\right)\left(x+1\right)\)
\(C=3x^2+7x+4=\left(x+1\right)\left(3x+4\right)\)
\(A=x^2+3x+2=\left(x+1\right)\left(x+2\right)\)
\(B=x^2-4x-5=\left(x-5\right)\left(x+1\right)\)
\(C=3x^2+7x+4=\left(x+1\right)\left(3x+4\right)\)
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: \(x^2-2xy+y^2-4m^2+4mn-n^2\)
\(=\left(x^2-2xy+y^2\right)-\left(4m^2-4mn+n^2\right)\)
\(=\left(x-y\right)^2-\left(2m-n\right)^2\)
\(=\left(x-y-2m+n\right)\left(x-y+2m-n\right)\)
a) \(4x\left(a-b\right)+6xy\left(b-a\right)\)
\(=4x\left(a-b\right)-6xy\left(a-b\right)\)
\(=\left(4x-6xy\right)\left(a-b\right)\)
\(=2x\left(2-3y\right)\left(a-b\right)\)
2x(x-2)+2y(x-2)= (x-2)(2x+2y)=2(x-2)(x+y)
b,2(xy+xyz-2x-2z)
c, 3(x^2-xy-x-y)
a) Ta có : 2x2 - 4x + 2xy - 4y
= 2x(x - 2) + 2y(x - 2)
= (x - 2)(2x + 2y)
= 2(x - 2)(x + y)