please help. This is the problem What is 39 squared?
There are many other ways to attack the problem, the box method which is long and tedious, simple multiplication, calculator... otherwise if you know the perfect square expansion:
39^2 = (40 - 1)^2... mainly cos 40 and 1 and nice numbers to work with.
= (40)^2 - 2*(40)*(-1) + 1^2
= 1600 + 80 + 1
= 1681
Sorry. Change of signs... it was nearly 3 am wen I posted it, what I meant was in fact:
$\displaystyle 39^2$
$\displaystyle = (40 - 1)^2$
$\displaystyle = 40^2 - 2 \times 40 \times 1 + 1^2$
$\displaystyle = 1600 - 80 + 1$
$\displaystyle = 1521$
Which IS the correct answer