a2-b2-2x(a-b) phân tích đa thức thành nhân tử
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a) x2 + xy –x – y = x(x + y) – (x + y) = (x + y)(x -1 ).
b) a2 – b2 + 8a + 16 = (a2 + 8a + 16) – b2 = (a + 4)2 – b2
= (a + 4 – b)(a + 4 + b).
.\(a\left(b^2+c^2\right)+b\left(c^2+a^2\right)+c\left(a^2+b^2\right)-2abc-a^3-b^3-c^3\)
=\(a\left(b^2-2bc+c^2-a^2\right)+b\left(a^2+2ac+c^2-b^2\right)+c\left(a^2-2ab+b^2-c^2\right)\)
=\(a\left[\left(b-c\right)^2-a^2\right]+b\left[\left(a+c\right)^2-b^2\right]+=c\left[\left(a-b^2\right)-c^2\right]\)
=\(a\left(c-b+a\right)\left(a+b-c\right)+b\left(a+c-b\right)\left(a+b+c\right)+c\left(a-b+c\right)\left(a-b-c\right)\)
=\(\left(a+c-b\right)\left[a\left(c-b+a\right)+b\left(a+b+c\right)+c\left(a-b-c\right)\right]\)
=\(\left(a+c-b\right)\left(b+a-c\right)\left(c+b-a\right)\)
\(=\left(b^2+c^2+2bc-a^2\right)\left(b^2+c^2-2bc-a^2\right)\)
\(=\left(b+c-a\right)\left(b+c+a\right)\left(b-c-a\right)\left(b-c+a\right)\)
a2 – b2 – 4a + 4
= a2 – 4a + 4 – b2
= (a – 2)2 – b2
= (a – 2 + b)(a – 2 – b)
= (a + b – 2)(a – b – 2)
a) \(a^2+ab-7a-7b=a\left(a+b\right)-7\left(a+b\right)=\left(a+b\right)\left(a-7\right)\)
b) \(5ab+4c+20b+ac=5b\left(a+4\right)+c\left(a+4\right)=\left(a+4\right)\left(5b+c\right)\)
c) \(a^2+6a-b^2+9=\left(a+3\right)^2-b^2=\left(a+b-b\right)\left(a+3+b\right)\)
d) \(a^2-16=\left(a-4\right)\left(a+4\right)\)
Lời giải:
$x^2-y^2+a^2-b^2+2ax+2by=(x^2+a^2+2ax)-(y^2+b^2-2by)$
$=(x+a)^2-(y-b)^2=(x+a-y+b)(x+a+y-b)$
\(a^2-b^2-2x\left(a-b\right)=\left(a-b\right)\left(a+b\right)-2x\left(a-b\right)=\left(a-b\right)\left(a+b-2x\right)\)
\(a^2-b^2-2x\left(a-b\right)\)
\(=\left(a-b\right)\left(a+b\right)-2x\left(a-b\right)\)
\(=\left(a-b\right)\left(a+b-2x\right)\)