Question

Multiply (in horizontal and vertical arrangement):

(11) (10m − 7n) (10m + 7n)

Answer 1

(10m − 7n) (10m + 7n)
Horizontal arrangement:
= (10m − 7n) × 10 m + (10m − 7n) × 7n
= 10m × 10m − 7n × 10m + 10m × 7n − 7n × 7n
= 100m² − 70nm + 70mn − 49n²
= 100m² − 49n²

Vertical arrangement:
$\begin{array}{c}\begin{array}{cccccc}& & & 10m& -& 7n\end{array}\\ \begin{array}{cccccc}& & \times & 10m& +& 7n\end{array}\\ \overline{\begin{array}{cccccc}& & & 70mn& -& 49n^2\end{array}}\\ \begin{array}{cccccc}+& 100m^2& -& 70mn& & \end{array}\\ \underline{\overline{\begin{array}{cccccc}& 100m^2& +& 0mn& -& 49n^2\end{array}}}\end{array}$