Question

Evaluate the following (using identities):

$98\times 99$

Answer 1

$98\times 99$
$=(100-2)(100-1)$
$={100}^2+(-2-1)\left(100\right)+(-2)(-1)$ [Using $(x+a)(x+b)=x^2+(a+b)x+ab$]
$=10000-300+2$
$=9702$