\(a,=4x^2+12x+9\\ b,=2x^2-\dfrac{2}{3}xy+\dfrac{1}{3}y^2\\ c,=\left(7x-1\right)^2+\left(7x+1\right)^2+2\left(7x-1\right)\left(7x+1\right)\\ =\left(7x-1+7x+1\right)^2=196x^2\\ d,=\left[\left(x+3\right)^2-y^2\right]:\left(x+y+3\right)\\ =\left(x+y+3\right)\left(x-y+3\right):\left(x+y+3\right)=x-y+3\)
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