# If a = 4 and b = -6, what is the value of the expression $$- {a^3} - {a^2}b + 7{b^2} - ab + 9?$$

125

Explanation

Working through each variable in  $$- {a^3} - {a^2}b + 7{b^2} - ab + 9$$ :
$$-a^{3}=-4^{3}=-6$$
$$-a^{2} b=-4^{2} \times-6=16 \times-6=-96$$
$$7 b^{2}=7 \times-6^{2}=7 \times 36=252$$
$$-ab = -4 \times -6 = 24$$
$$-64 + -96 + 252 + 24 + 9 = 125$$