Really easy maths question...

hellarda · 3 Jan 2012 at 12:28

Hello,

Just attempting one of my c1 papers I've had to do over the holidays and there is one question which is really stumping me... I have looked over it and convinced I have the right answer but the markscheme says otherwise :/

Question is solve the simultaneous equations

x+y=2 and 3x^2-2x+y^2=2

So you sub in y=2-x into the 2nd equ and then need to expand

3x^2-2x+(2-x)^2=2

To which I get:
2x^2-6x+2=0

But the markscheme says:
2x^2-3x+1=0

What am I doing wrong? Someone explain pleeeease

Cheers guys

Ricochet J · 3 Jan 2012 at 12:33

The mark scheme is correct.

x+y=2
3x^2-2x+y^2=2

From Eq 1, y=2-x

Substitute into Eq 2.

3x^2-2x+(2-x)^2=2

Which becomes

3x^2-2x+4-4x+x^2=2

Which reduces to

4x^2-6x+2=0

Which cancels down to

2x^2-3x+1=0

hellarda · 3 Jan 2012 at 12:35

Ricochet J said:
The mark scheme is correct.

Thanks I had gathered. But how do I get to that answer?!

Ricochet J · 3 Jan 2012 at 12:37

Edit. Ignore this post.

Nitefly · 3 Jan 2012 at 12:37

(2-x)^2 = x^2 -4x +4

Are you sure you are adding the different components together correctly?

Nitefly · 3 Jan 2012 at 12:39

Ricochet J said:
Edit. Ignore this post.

Nope, he only had 2x^2.

Haha you ninja!

andrewdodd13 · 3 Jan 2012 at 12:39

Just a helpful hint - Alt+0178 gives ² and 0179 gives ³. They just make it a bit nicer to read really

Ricochet J · 3 Jan 2012 at 12:39

Nitefly said:
Nope, he only had 2x^2.

I gathered that afterward which is why I ninja edited

Jay794 · 3 Jan 2012 at 12:43

I took one look at this and I just saw the numbers melt off the page lol

Ricochet J · 3 Jan 2012 at 12:49

Jay794 said:
I took one look at this and I just saw the numbers melt off the page lol

It's really not hard. Write it down on some scrap paper and you'll see it's a piece of cake.

hellarda · 3 Jan 2012 at 12:50

Nitefly said:
(2-x)^2 = x^2 -4x +4

Are you sure you are adding the different components together correctly?

Yep I forgot the double minus on the x so I got -x^2 instead of + which now makes ricochets answer make sense

thank youuss

Reaper 392 · 3 Jan 2012 at 12:51

andrewdodd13 said:
Just a helpful hint - Alt+0178 gives ² and 0179 gives ³. They just make it a bit nicer to read really

this makes it even nicer: http://www.forkosh.com/mimetextutorial.html

*edit*
never mind, you seem happy with what you have

Jay794 · 3 Jan 2012 at 13:36

Ricochet J said:
It's really not hard. Write it down on some scrap paper and you'll see it's a piece of cake.

Maths is not my strong point, thats what calculators are for, if I can't work something out, e.g how much something costs in a foreign country, I just pull out my biggest note lol

RomanNose · 3 Jan 2012 at 13:52

Jay794 said:
Maths is not my strong point, thats what calculators are for, if I can't work something out, e.g how much something costs in a foreign country, I just pull out my biggest note lol

Arithmetic!=maths.