pls help me!!! plsss

hi every1 pls sum 1 help me with this quadratic equation its rele buggin me now lol!!
15-10x-x^2

okay so ive tried rearranging it to:

-x^2-10+15 i am getin right numbers bt rong answer can u pls just xplain it 2 me in layman terms lol

the answer is -[(x+5)^2 - 40]

but how the hell du get 2 tht..thnks in advance :wink:

Reply 1

BJack

The maths help forum is f38.

You'll find people are more likely to help you if post there in English.

Reply 2

I Have No Imagination

Well 15 - 10x - x^2 = 0

Therefore rearranging means you take everything to the other side, which equals;

x^2 + 10x - 15 = 0

Then you have to complete the square, I'm sure you know how to do that?

Reply 3

stibbit

I cant help you with this, but I can help you learn to spell and use capital letters.

Reply 4

saxty

May as well help you now it's here. The first thing I would do is factorise by minus one, so you end up with -(x^2 + 10x - 15). Then use completing the square, I end up with -((x+5)^2)) which gives the right amount of x's and x squareds. However, I end up with a constant of 25 instead of -15, so minus 40 to get back to the original equation.. -((x+5)^2 - 40)