==========================================================
$\left(-\dfrac{1}{3}ab^2c\right)^3 = -\dfrac{1}{27}a^3b^6c^3;$
$\left(+\dfrac{3}{5}a^4b^2c^2\right)^3 = +\dfrac{27}{125}a^{12}b^6c^6;$
$\left(+\dfrac{9}{2}x^4y^5\right)^2 = +\dfrac{81}{4}x^8y^{10};$
$\left(-\dfrac{9}{4}a^5b^3c \right)^2 = +\dfrac{81}{16}a^{10}b^6c^2.$