# Thread: I'm not understanding this problem

1. ## I'm not understanding this problem

2. Originally Posted by Angel King
39 squared = 39^2 = 39 * 39 = 1521

-Dan

3. Originally Posted by Angel King
I think we would be interested in why you find this a problem?

Is it that you don't know what 39 squared means? ( it means 39 times itself
which is 39x39).

Or that you cant do the multiplication?

RonL

4. 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

5. Originally Posted by AlvinCY
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
Except we do hope to get the right answer

RonL

6. Sorry. Change of signs... it was nearly 3 am wen I posted it, what I meant was in fact:

$39^2$
$= (40 - 1)^2$
$= 40^2 - 2 \times 40 \times 1 + 1^2$
$= 1600 - 80 + 1$
$= 1521$