Hello,Originally Posted bymacca101

you've got this:

. Rearrange to:

Notice that there is a negative sign before the 2nd paranthese. Therefore the 9 which isaddedin the paranthese to get a complete square is actually subtracted. So you added 4 and subtracted 9 on the LHS of the equation and therefore you have to do the same on the RHS too.

You'll get:

Greetings

EB