Expanding 1/2(x-3)^2-18: why do I get -27 instead of -27/2?

[Schrodinger's Dog]

I have the equation 1/2(x-3)^2-18

Now normally I have no trouble with expansion of brackets but for some reason this is puzling to me.

1/2x^2-3x-9-18

I get 1/2x^2-3x-27

I checked the answer with a maths package and it comes up with : -

1/2x^2-3x-27/2 Why? What am I missing here. where does the 27/2 come in?

I also get 1/2(x-3)(x-9) if I factorise it again? My pacckage obviously likes, multiple different factorisations.

Anyway I'm a bit stumped, normally I don't have a problem with this sort of straightforward stuff but I'm stumped on this one?

 

[0rthodontist]

To clarify, your expression is
(1/2)*(x-3)^2-18

What do you get when you expand (x-3)^2? You're then going to want to take half of that ENTIRE expression (which means half of every term in it) and subtract 18 from your result.

 

[Schrodinger's Dog]

To clarify, your expression is
(1/2)*(x-3)^2-18

What do you get when you expand (x-3)^2? You're then going to want to take half of that ENTIRE expression (which means half of every term in it) and subtract 18 from your result.

It is official I am an idiot of course -13.5 =-27/2 (+4.5-18) thanks