Phân tích đa thức thành nhân tử.
(x + y)^5 – x^5 – y^5
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Ta có:
\(\left(x+y\right)^5-x^5-y^5=\left(x+y\right)^5-\left(x^5+y^5\right)\)
\(=\left(x+y\right)^5-\left(x+y\right)\left(x^4-x^3y+x^2y^2-xy^3+y^4\right)\)
\(=\left(x+y\right)\left[\left(x+y\right)^4-x^4+x^3y-x^2y^2+xy^3-y^4\right]\)
\(=\left(x+y\right)\left[x^4+4x^3y+6x^2y^2+4xy^3+y^4-x^4+x^3y-x^2y^2+xy^3-y^4\right]\)
\(=\left(x+y\right)\left(5x^3y+5x^2y^2+5xy^3\right)=5xy\left(x+y\right)\left(x^2+xy+y^2\right)\)
\(1,\\ 1,=15\left(x+y\right)\\ 2,=4\left(2x-3y\right)\\ 3,=x\left(y-1\right)\\ 4,=2x\left(2x-3\right)\\ 2,\\ 1,=\left(x+y\right)\left(2-5a\right)\\ 2,=\left(x-5\right)\left(a^2-3\right)\\ 3,=\left(a-b\right)\left(4x+6xy\right)=2x\left(2+3y\right)\left(a-b\right)\\ 4,=\left(x-1\right)\left(3x+5\right)\\ 3,\\ A=13\left(87+12+1\right)=13\cdot100=1300\\ B=\left(x-3\right)\left(2x+y\right)=\left(13-3\right)\left(26+4\right)=10\cdot30=300\\ 4,\\ 1,\Rightarrow\left(x-5\right)\left(x-2\right)=0\Rightarrow\left[{}\begin{matrix}x=2\\x=5\end{matrix}\right.\\ 2,\Rightarrow\left(x-7\right)\left(x+2\right)=0\Rightarrow\left[{}\begin{matrix}x=7\\x=-2\end{matrix}\right.\\ 3,\Rightarrow\left(3x-1\right)\left(x-4\right)=0\Rightarrow\left[{}\begin{matrix}x=\dfrac{1}{3}\\x=4\end{matrix}\right.\\ 4,\Rightarrow\left(2x+3\right)\left(2x-1\right)=0\\ \Rightarrow\left[{}\begin{matrix}x=-\dfrac{3}{2}\\x=\dfrac{1}{2}\end{matrix}\right.\)
\(\left(x+y\right)^5-x^5-y^5=x^5+5x^4y+10x^3y^2+10x^2y^3+5xy^4+y^5-x^5-y^5=5x^4y+10x^3y^2+10x^2y^3+5xy^4=5xy\left(x^3+2x^2y+2xy^2+y^3\right)\)