mathematics make you crazy isn't it?

then you need refresh your brain !

and sing this song . 

PO PO PO 
PO NE NE
NE PO NE
NE NE PO

you know what the meaning of PO and NE?

PO mean POSITIVE and

NE stand for NEGATIVE.

easy to rote isn't it?

when you sing this song, you also studying about mathematic.

try it.  it will be fun. trust me :)