\(9a^2-\left(2a-b\right)^2=\left(3a\right)^2-\left(2a-b\right)^2=\left(3a-2a+b\right)\left(3a+2a-b\right)=\left(a+b\right)\left(5a-b\right)\)
\(x^2-2x-15=x^2-5x+3x-15=x\left(x-5\right)+3\left(x-5\right)=\left(x-5\right)\left(x+3\right)\)
\(xy+\dfrac{1}{3}y-\dfrac{1}{4}x-\dfrac{1}{12}=y\left(x+\dfrac{1}{3}\right)-\dfrac{1}{4}\left(x+\dfrac{1}{3}\right)=\left(x+\dfrac{1}{3}\right)\left(y-\dfrac{1}{4}\right)\)
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