Question

Using identities, evaluate ${12.1}^2-{7.9}^2$.

• A. $84$
• B. $72$
• C. $69$
• D. $87$

Answer 1

The correct option is A $84$

Given, $(12.1{)}^2-(7.9{)}^2$.

We know, $(a^2-b^2)=(a+b)(a-b)$.

Then,

$(12.1{)}^2-(7.9{)}^2$

$=(12.1+7.9)(12.1-7.9)$

$=20\times 4.2$

$=84$.

Therefore, option $A$ is correct.