a^2 -ab + a - b
5y^2 - 10yz + 5z^2
3x^2 - 12y^2
ab - b + a^2 - a
x^2 - x - 6
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a)\(x^6-y^6=\left(x^3-y^3\right)\left(x^3+y^3\right)\)
\(=\left(x-y\right)\left(x^2+xy+y^2\right)\left(x+y\right)\left(x^2-xy+y^2\right)\)
\(x^2+9x-y^2-9=saide\)
\(a^2-14a-9b^2+49=\left(a-3b-7\right)\left(a+3b-7\right)\)
\(9-a^2-2ab-b^2=-\left(a+b-3\right)\left(a+b+3\right)\)
\(x^2-10x-y^2+10y=\left(x-y\right)\left(x+y-10\right)\)
\(a^2+2ab+b^2-81=\left(a+b-9\right)\left(a+b+9\right)\)
\(x^2-y^2+5x-5y=\left(x-y\right)\left(x+y+5\right)\)
a: \(x^2-y^2+10yz-25z^2\)
\(=x^2-\left(y^2-10yz+25z^2\right)\)
\(=x^2-\left(y-5z\right)^2\)
\(=\left(x-y+5z\right)\left(x+y-5z\right)\)
\(A=2y-x-\left\{2x-y-\left[y+3x-\left(5y-x\right)\right]\right\}\)
\(=2y-x-\left\{2x-y-\left[y+3x-5y+x\right]\right\}\)
\(=2y-x-\left\{2x-y-y-3x+5y-x\right\}\)
\(=2y-x-2x+y+y+3x-5y+x\)
\(=\left(2y+y+y-5y\right)+\left(-x-2x+3x+x\right)\)
= \(-y+x\)
Thay \(x=a^2+2ab+b^2,y=a^2-2ab+b^2\) vào đa thức -y + x :
\(-\left(a^2-2ab+b^2\right)+\left(a^2+2ab+b^2\right)\)
\(=-a^2+2ab-b^2+a^2+2ab+b^2\)
\(=\left(-a^2+a^2\right)+\left(2ab+2ab\right)+\left(-b^2+b^2\right)\)
= 4ab
\(A=2y-x-\left\{2x-y-\left[y+3x-\left(5y-x\right)\right]\right\}\\ =2y-x-\left\{2x-y-y-3x+5y-x\right\}\\ =2y-x-2x+y+y+3x-5y+x\\ =-y+x=-\left(a^2-2ab+b^2\right)+\left(a^2+2ab+b^2\right)\\ =-a^2+2ab-b^2+a^2+2ab+b^2=4ab\)
a2 - ab + a - b = (a2 - ab) + (a - b) = a(a - b) + (a - b) = (a - b)(a + 1)
5y2 - 10yz + 5z2 = 5(y2 -2yz + z2) = 5(y - z)2
3x2 - 12y2 = 3(x2 - 4y2) = 3(x - 2y)(x + 2y)
ab - b + a2 - a = (ab + a2) - (a + b) = a(a + b) - (a + b) = (a + b)(a - 1)
x2 - x - 6 = x2 + 2x - 3x - 6 = x(x + 2) - 3(x + 2) = (x + 2)(x - 3)