Question

Evaluate $55\times 45$ using suitable identity.

Answer 1

Using Formula $(x+a)(x+b)$ = $x^2+(a+b)x+ab$
Writing $55as50+5$ and $45as50-5$
$\Rightarrow$ $(50+5)(50-5)$ = ${50}^2+[5+(-5\left)\right]50+\left(5\right)(-5)$
$=$ $2500+\left(0\right)50-25$
$=$ $2475$
The answer is $2475$