Tính:
a) \( (2x^2+3y)^3;\) b) \((\dfrac12x−3)^3\)
\(a) (2x^2+3y)^3=(2x^2)^3+3(2x^2)^2.3y+3.2x^2.(3y)^2+(3y)^3\)
\(=8x^6+36x^4y+54x^2y^2+27y^3\)
\(b) (\dfrac{1}{2}x−3)^3=(\dfrac{1}{2}x)^3−3(\dfrac{1}{2}x)^2.3+3(\dfrac{1}{2}x).3^2−3^3\)
\(=\dfrac18x^3−\dfrac94x^2+\dfrac{27}2x−27\)
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