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Ответ:

Применяем формулы сокращённого умножения:

 [tex]\bf (a-b)^2=a^2-2ab+b^2\ \ ,\ \ \ (a-b)^3=a^3-3a^2b+3ab^2-b^3[/tex]   .

[tex]\bf a)\ \ (\ \boxed{\ {}^{}\ }-\boxed{\ {}^{}\ }\ )^2=4x^2-12x+\boxed{\ {}^{}\ }\\\\\Big(\ \boxed{\bf \, 2x\, }-\boxed{\bf \, 3\, }\ \Big)^2=(2x)^2-2\cdot 2x\cdot 3+3^2=4x^2-12x+\boxed{\bf \ 9\ }\\\\\\b)\ \ (\ x-\boxed{\ {}^{}\ }\ )^3=\boxed{\ {}^{}\ }-6x^2y+\boxed{\ {}^{}\ }-8y^3\\\\\Big(\ x-\boxed{\bf \, 2y\, }\ \Big)^3=x^3-3\cdot x^2\cdot 2y+3\cdot x\cdot 4y^2-(2y)^3=\boxed{\bf \, x^3\, }-6x^2y+\boxed{\bf \, 12xy^2}-8y^3[/tex]