Question

Multiply (in vertical and horizontal arrangement):

(4) (5a² – 3b²) × 4ab

Answer 1

(4) (5a² – 3b²) × 4ab
Vertical arrangement:
$\begin{array}{c}\begin{array}{cccc}& 5a^2& -& 3b^2\end{array}\\ \begin{array}{cccc}\times & & & 4ab\end{array}\\ \overline{\underline{\begin{array}{cccc}& 20a^{3}b& -& 12a{b}^3\end{array}}}\end{array}$
Horizontal arrangement:
(5a² – 3b²) × 4ab
= (4ab × 5a²) – (4ab × 3b²)
= (4 × a × b × 5 × a × a) – (4 × a × b × 3 × b × b)
= ((4 × 5) × (a × a × a) × b) – ((4 × 3) × a × (b × b × b))
= 20a³b – 12ab³