Question

Question 8(iii)
Using $(x+a)(x+b)=x^2+(a+b)x+ab$, find
$103\times 98$

Answer 1

$103\times 98=(100+3)\times (100-2)$
$=(100{)}^2+(3-2)\times 100+3\times (-2)$
$\left[Usingidentity\right(x+a\left)\right(x+b)=x^2+(a+b)x+ab]$
$=10000+(3-2)\times 100-6$
$=10000+100-6=10094$