Question

Evaluate.

(78 x 82)

Answer 1

$$\begin{gathered} 78\times 82 \\ =\left(80-2\right)\left(80+2\right) \\ ={\left(80\right)}^2-2^2\{\mathrm{using}\mathrm{the}\mathrm{identity}\left(a-b\right)\left(a+b\right)=a^2-b^2\} \\ =6400-4 \\ =6396 \end{gathered}$$