Question

using identities :express 39^2

Answer 1

(40-1)²=by a²-2ab+b²+(40)²-2×40×1+(1)²=1600-80+1 =1520+1=1521
$is \: your \: answer$

Answer 2

(40-1) square
a-b the whole square=a square+b square-2ab
40 square+1 square-2×40×1
1600+1-80
1601-80
= 1521