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\(\left(a+b+c\right)^3-a^3-b^3-c^3\)
\(=\left(a+b\right)^3+3c\left(a+b\right)\left(a+b+c\right)+c^3-a^3-b^3-c^3\)
\(=a^3+b^3+c^3+3ab\left(a+b\right)+3c\left(a+b\right)\left(a+b+c\right)-a^3-b^3-c^3\)
\(=3\left(a+b\right)\left[ab+c\left(a+b+c\right)\right]\)
\(=3\left(a+b\right)\left(ab+ac+bc+c^2\right)\)
\(=3\left(a+b\right)\left(b+c\right)\left(c+a\right)\)
\(\left(a+b+c\right)^3-a^3-b^3-c^3\)
\(=a^3+b^3+c^3+3\left(a+b\right)\left(b+c\right)\left(c+a\right)-a^3-b^3-c^3\)
\(=3\left(a+b\right)\left(b+c\right)\left(c+a\right)\)
a) bt \(=\left(x-8\right)\left(x^2-x-2\right)=\left(x-8\right)\left(x+1\right)\left(x-2\right)\)
kl: ...
b) \(=\left(x+2\right)\left(x^2-8x-15\right)=\left(x+2\right)\left(x-5\right)\left(x-3\right)\)
kl:....
a, \(x^3-9x^2+6x+16\)
\(=x^3-8x^2-x^2+8x-2x+16\)
\(=x^2\left(x-8\right)-x\left(x-8\right)-2\left(x-8\right)\)
\(=\left(x-8\right)\left(x^2-x-2\right)\)
\(=\left(x-8\right)\left(x^2-2x+x-2\right)\)
\(=\left(x-8\right)\left[x\left(x-2\right)+\left(x-2\right)\right]\)
\(=\left(x-8\right)\left(x-2\right)\left(x+1\right)\)
b, \(x^3-6x^2-x+30\)
\(=x^3-5x^2-x^2+5x-6x+30\)
\(=x^2\left(x-5\right)-x\left(x-5\right)-6\left(x-5\right)\)
\(=\left(x-5\right)\left(x^2-x-6\right)\)
\(=\left(x-5\right)\left(x^2-3x+2x-6\right)\)
\(=\left(x-5\right)\left[x\left(x-3\right)+2\left(x-3\right)\right]\)
\(=\left(x-5\right)\left(x-3\right)\left(x+2\right)\)
Chúc bạn học tốt!!!
\(x^6-x^4-9x^3+9x^2\)
\(=x^6-x^5+x^5-x^4-9x^2\left(x-1\right)\)
\(=x^5\left(x-1\right)+x^4\left(x-1\right)-9x^2\left(x-1\right)\)
\(=\left(x-1\right)\left(x^5+x^4-9x^2\right)\)
\(x^6-x^4-9x^3+9x^2\)
\(=x^4.\left(x^2-1\right)-9x^2\left(x-1\right)\)
\(=x^4.\left(x-1\right)\left(x+1\right)-9x^2\left(x-1\right)\)
\(=\left(x-1\right)\left[x^4.\left(x+1\right)-9x^2\right]\)
-x3+9x2-27x+27
-x3+3x2+6x2-18x-9x+27
-x2(x-3)+6x(x-3)-9(x-3)
(-x2+6x-9)(x-3)
-(x2-6x+9)(x-3)
-(x-3)3
x6 - x4 - 9x3 + 9x2
= x4.(x2 - 1) - 9x2.(x - 1)
= x4.(x - 1).(x + 1) - 9x2.(x - 1)
= (x - 1).(x5 + x - 9x2)
= (x - 1).x.(x4 + 1 - 9x)
x^6-x^4-9x^3+9x^2
=x^2(x^4-x^2-9x+9)
=x^2[x^2(x^2-1)-9(x-1)]
=x^2[x^2(x-1)(x+1)-9(x-1)]
=x^2(x-1)[x^2(x+1)-9)]
=x^2(x-1)(x+1)(x^2-9)
=x^2(x-1)(x+1)(x-3)(x+3)
\(x^3+x^2+9x-10x^2-10x+25x+25\)
\(=x^2\left(x+1\right)-10x\left(x+1\right)+25\left(x+1\right)\)
\(=\left(x+1\right)\left(x^2-10x+25\right)=\left(x+1\right)\left(x-5\right)^2\)
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