Question

Solve the problem using direct multiplication method to find the square of $99$.

Answer 1

We can write ${99}^2=(100-1{)}^2$

Using $(a-b{)}^2=a(a-b)-b(a-b)$
Here $a=100,b=1$
Therefore, ${99}^2=100(100-1)-1(100-1)$
$=$ ${100}^2-100-100+1^2$
$=10000-200+1$
$=9801$