\(a,4x+4y\)
\(=4\left(x+y\right)\)
b,\(2xy-y^2+2x-y\)
\(=\left(2xy+2x\right)-\left(y^2+y\right)\)
\(=2x\left(y+1\right)-y\left(y+1\right)\)
\(=\left(y+1\right)\left(2x-y\right)\)
\(c,2x^3y-8x^2y^2+8xy^3\)
\(=2xy\left(x^2-4xy+4y^2\right)\)
\(=2xy\left(x^2-2.x.2y+\left(2y\right)^2\right)\)
\(=2xy\left(x-2y\right)^2\)
Bai 2:
\(a,x^2-81=0\)
\(\Rightarrow x^2-9^2=0\)
\(\Rightarrow\left(x-9\right)\left(x+9\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x-9=0\\x+9=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=9\\x=-9\end{matrix}\right.\)
\(b,x^2+x-6=0\)
\(\Rightarrow x^2+3x-2x-6=0\)
\(\Rightarrow\left(x^2-2x\right)+\left(3x-6\right)=0\)
\(\Rightarrow x\left(x-2\right)+3\left(x-2\right)=0\)
\(\Rightarrow\left(x-2\right)\left(x+3\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x-2=0\\x+3=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=2\\x=-3\end{matrix}\right.\)
Bai3:
\(A=19^{n+1}-19^n\)
\(=19^n.19-19^n\)
\(=19^n\left(19-1\right)\)
\(=19^n.18\)
Vif \(18⋮18\Rightarrow19^n.18⋮18\)
Hay A \(⋮\) 18
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