Answer
$-12x^6 + 40x^4$
Work Step by Step
(i) $a^m \cdot a^n = a^{m+n}$
(ii) $x(y-z) = xy - xz$
Use rule (ii) above by multiplying $-4x^3$ to each term of the binomial to obtain:
$=-4x^3(3x^3) - (-4x^3)(10x)$
Multiply the coefficients together, and then apply rule (i) above to obtain:
$\\=-12x^{3+3}-(-40x^{3+1})
\\=-12x^6-(-40x^4)
\\=-12x^6 + 40x^4$
