Question

Which of the following identity can be used to solve $1001\times 999$?

• A. (a + b) (a - b) = -
• B. = + 2ab +
• C. = - 2ab +
• D. = + 3 + 3 +

Answer 1

The correct option is A

(a + b) (a - b) = -

1001 = (1000 + 1)
999 = (1000 - 1)
$(1000+1)(1000-1)={1000}^2-1^2$
$\left[Using\right[(a+b)\times (a-b)=a^2-b^2]$

$=1000000-1=999999$
So, we used the identity
[$(a+b)\times (a-b)=a^2-b^2$] to solve the quesion.