Question

Multiply (in vertical and horizontal arrangement):

(5) (5m²n – n²) × 4mn

Answer 1

(5) (5m²n – n²) × 4mn
Vertical arrangement:
$\begin{array}{c}\begin{array}{cccc}& 5m^{2}n& -& n^2\end{array}\\ \begin{array}{cccc}\times & & & 4mn\end{array}\\ \overline{\underline{\begin{array}{cccc}& 20m^3{n}^2& -& 4m{n}^3\end{array}}}\end{array}$
Horizontal arrangement:
(5m²n – n²) × 4mn
= (4mn × 5m²n) – (4mn × n²)
= (4 × m × n × 5 × m × m × n) – (4 × m × n × n × n)
= ((4 × 5) × (m × m × m)×(n × n)) – (4 × m × (n × n × n))
= 20m³n² – 4mn³