Question

Find the square of the following numbers without actual multiplication
$39$

Answer 1

Consider the given number.

$39$

We know that

${(a-b)}^2=a^2+b^2-2ab$

Therefore,

${(40-1)}^2={\left(40\right)}^2+1^2-2\times 40\times 1$

${\left(39\right)}^2=1600+1-80$

${\left(39\right)}^2=1521$

Hence, this is the answer.