Đáp án:
$a, (3a+1)^3$
$ = (3a+1)(3a+1)^2$
$ = (3a+1)(9a^2+6a+1)$
$ = 27a^3 + 18a^2 + 3a+9a^2+6a+1$
$ = 27a^3+27a^2+9a+1$
$b, (4-2b)^3$
$ = (4-2b)(4-2b)^2$
$ = (4-2b)(16-16b+4b^2)$
$ = 64 - 64b+16b^2-32b+32b^2-8b^3$
$ = 64 -96b+48b^2-8b^3$
$c,(2c-3d)^3$
$ = (2c-3d)(2c-3d)^2$
$ = (2c-3d)(4c^2-12cd+9d^2)$
$ = 8c^3 - 24c^2d+18cd^2-12c^2d+36cd^2-27d^3$
$= 8c^3 - 36c^2d + 54cd^2 - 27d^3$
$d, (\dfrac{3}{y} - \dfrac{2y}{x})^3$
$= (\dfrac{3}{y} - \dfrac{2y}{x})(\dfrac{3}{y} - \dfrac{2y}{x})^2$
$ = (\dfrac{3}{y} - \dfrac{2y}{x}) . (\dfrac{9}{y^2} - \dfrac{12y}{xy} + \dfrac{4y^2}{x^2})$
$ = \dfrac{27}{y^3} - \dfrac{36y}{xy^2} + \dfrac{12y^2}{x^2y} -\dfrac{18y}{xy^2} + \dfrac{24y^2}{x^2y} -\dfrac{8y^3}{x^3}$
$ = \dfrac{27}{y^3} - \dfrac{54y}{xy^2} + \dfrac{36y^2}{x^2y} -\dfrac{8y^3}{x^3}$
