k) \(x^2-xy-6x+9+3y\)
\(=x^2-6x+9-xy+3y\)
\(=\left(x^2-6x+9\right)-\left(xy-3y\right)\)
\(=\left(x-3\right)^2-y\left(x-3\right)\)
\(=\left(x-3\right)\left[\left(x-3\right)-y\right]\)
\(=\left(x-3\right)\left(x-3-y\right)\)
l) \(x^2+4-y^2+4x\)
\(=x^2+4x+4-y^2\)
\(=\left(x^2+4x+4\right)-y^2\)
\(=\left(x+2\right)^2-y^2\)
\(=\left(x+2-y\right)\left(x+2+y\right)\)
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k: =(x^2-6x+9)-y(x-3)
=(x-3)^2-y(x-3)
=(x-3)(x-3-y)
l: =(x^2+4x+4)-y^2
=(x+2)^2-y^2
=(x+2+y)(x+2-y)
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