Question

Determine the square value of $813$ using direct multiplication method.

Answer 1

We can write ${813}^2=(800+13{)}^2$

Using $(a+b{)}^2=a(a+b)+b(a+b)$
Here $a=800,b=13$
Therefore, ${813}^2=800(800+13)+13(800+13)$
$={800}^2+10400+10400+{13}^2$
$=640000+20800+169$
$=660969$