Question

By using identity.
${\left(799\right)}^2=?$

Answer 1

$(799{)}^2$

we can write as

$(799{)}^2=(800-1{)}^2$

using identity

$(A-B{)}^2=A^2+B^2-2AB$

$(800-1{)}^2={800}^2+1^2-2\times 800\times 1$

$=640000+1-1600$

($799{)}^2=638401$

Hence this is the answer