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Ta có
4 x 2 y − 2 x y 2 + 1 3 x 2 y − x + 2 x 2 y + x y 2 − 1 3 x − 6 x 2 y = 4 x 2 y + 1 3 x 2 y + 2 x 2 y − 6 x 2 y + − 2 x y 2 + x y 2 + − 1 3 x − x = 1 3 x 2 y − x y 2 − 4 3 x
Chọn đáp án B
x2y + 2x2y + 3x2y + 4x2y + .... + nx2y = 55x2y
\(\Rightarrow x^2y\left(1+2+...+n\right)=55x^2y\)
\(\Rightarrow1+2+...+n=55\)
\(\Rightarrow\dfrac{\left(\dfrac{n-1}{1}+1\right).\left(n+1\right)}{2}=55\)
\(\Rightarrow n\left(n+1\right)=55.2=110\)
\(\Rightarrow n^2+n-110=0\)
\(\Rightarrow n^2-10n+11n-110=0\)
\(\Rightarrow n\left(n-10\right)+11\left(n-10\right)=0\)
\(\Rightarrow\left(n-10\right)\left(n+11\right)=0\)
\(\Rightarrow n-10=0\) hay \(n+11=0\)
\(\Rightarrow n=10\left(nhận\right)\) hay \(n=-11\left(loại\right)\)
\(1,\\ 12x^6y^3:4x^3y=3x^3y^2\\ \left(x+1\right)\left(x^2-x+1\right)=x^3+1\\ 2x^2y\left(x^2+3xy\right)=3x^4y+6x^3y^2\\ 2,\\ a,=2xy\left(2x+3y-4\right)\\ b,=\left(x-3\right)\left(x+y\right)\\ c,=\left(x-2\right)\left(x+2\right)+y\left(x-2\right)=\left(x+y+2\right)\left(x-2\right)\\ d,=x^2-2x-5x+10=\left(x-2\right)\left(x-5\right)\\ 3,\\ a,\Leftrightarrow x^2-x^2+2x=2\\ \Leftrightarrow2x=2\Leftrightarrow x=1\\ b,\Leftrightarrow\left(x-2\right)\left(x-2+1\right)=0\\ \Leftrightarrow\left(x-2\right)\left(x-1\right)=0\Leftrightarrow\left[{}\begin{matrix}x=1\\x=2\end{matrix}\right.\)
\(a,=x\left(x-2\right)\\ b,=2b\left(x-3y\right)+a\left(x-3y\right)=\left(a+2b\right)\left(x-3y\right)\\ c,=x\left(x^2+2xy+y^2-4\right)=x\left[\left(x+y\right)^2-4\right]=x\left(x+y+2\right)\left(x+y-2\right)\\ d,=4-\left(x+y\right)^2=\left(2-x-y\right)\left(2+x+y\right)\\ đ,=5\left(x-y\right)\left(x+y\right)+3\left(x+y\right)^2=\left(x+y\right)\left(5x-5y+3x+3y\right)\\ =\left(x+y\right)\left(8x-2y\right)=2\left(4x-y\right)\left(x+y\right)\\ e,=3x\left(2xy-3\right)\\ b,=x\left(4x^2-4xy+y^2-4\right)=x\left[\left(2x-y\right)^2-4\right]=x\left(2x-y-2\right)\left(2x-y+2\right)\\ f,=\left(x+y\right)^2-z^2=\left(x+y-z\right)\left(x+y+z\right)\)
\(4x^2y+7x^2y-6x^2y-3x^2y\)
\(=\left(4+7-6-3\right)x^2y\)
\(=2x^2y\)
Thay x = 2, y = -3 vào đơn thức ta có A = -(2.2)2.(-3) = 24. Chọn C
= - 4x2y là:
