\(\left(x+\dfrac{1}{6}y+3\right)^2\)
\(=x^2+\dfrac{1}{36}y^2+9+2x\cdot\dfrac{1}{6}y+2x\cdot3+2\cdot3\cdot\dfrac{1}{6}y\)
\(=x^2+\dfrac{1}{36}y^2+9+\dfrac{1}{3}xy+6x+y\)
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