# Thread: qaudratic eqautions

1. ## qaudratic eqautions

X-2=10
X(SQAURED)+Y(SQAURED)=20

I cant seem to get the formula to work...keeps on coming out uneven!!!

2. Originally Posted by ENNO
X-2=10
X(SQAURED)+Y(SQAURED)=20

I cant seem to get the formula to work...keeps on coming out uneven!!!
check your question again. it makes no sense to write x - 2 = 10. why not just write x = 12?

3. Originally Posted by Jhevon
check your question again. it makes no sense to write x - 2y = 10. why not just write x = 12?
because I just took it straight from the book...this doesnt help my problem in any way!

4. Originally Posted by ENNO
because I just took it straight from the book...this doesnt help my problem in any way!
ok. i think you need to provide more info. because i don't see what you want to do here. it seems you want to solve the equations simultaneously, but then the solution for x is given in the first equation which makes the problem trivial. simply substitute x = 12 into the second equation to solve for y. the problem is stupid, unless i am misinterpreting the directions and/or you made a typo

5. Originally Posted by Jhevon
ok. i think you need to provide more info. because i don't see what you want to do here. it seems you want to solve the equations simultaneously, but then the solution for x is given in the first equation which makes the problem trivial. simply substitute x = 12 into the second equation to solve for y. the problem is stupid, unless i am misinterpreting the directions and/or you made a typo
yes I did...it is a simultaneous eqaution...sorry bout that!

And alos it is a 2y...

6. Originally Posted by ENNO
yes I did...it is a simultaneous eqaution...sorry bout that!

And alos it is a 2y...
so you did make a typo!

well, anyway. keep the same game plan. from the first equation then, x = 10 + 2y

plug this in for x in the second equation and solve for y. then you can find x

7. Originally Posted by Jhevon
so you did make a typo!

well, anyway. keep the same game plan. from the first equation then, x = 10 + 2y

plug this in for x in the second equation and solve for y. then you can find x
Thats my problem,

I can work it out into a qaudratic formula but it doesnt work out!

80-40y-5y(sqaured)=0....when I plug it into the qaudratic formula i get crazy answers!

8. Originally Posted by ENNO
Thats my problem,

I can work it out into a qaudratic formula but it doesnt work out!

80-40y-5y(sqaured)=0....when I plug it into the qaudratic formula i get crazy answers!
ok, we have:

$x - 2y = 10$ .................(1)
$x^2 + y^2 = 20$ ...........(2)

From (1), $x = 10 + 2y$, plug this into (2), we get:

$(10 + 2y)^2 + y^2 = 20$

$\Rightarrow 100 + 40y + 4y^2 + y^2 = 20$

$\Rightarrow 5y^2 + 40y + 80 = 0$

$\Rightarrow y^2 + 8y + 16 = 0$

this is a perfect square, we don't even need the quadratic formula here

$\Rightarrow (y + 4)^2 = 0$

$\Rightarrow y = -4$

now continue

9. Originally Posted by Jhevon
ok, we have:

$x - 2y = 10$ .................(1)
$x^2 + y^2 = 20$ ...........(2)

From (1), $x = 10 + 2y$, plug this into (2), we get:

$(10 + 2y)^2 + y^2 = 20$

$\Rightarrow 100 + 40y + 4y^2 + y^2 = 20$

$\Rightarrow 5y^2 + 40y + 80 = 0$

$\Rightarrow y^2 + 8y + 16 = 0$

this is a perfect square, we don't even need the quadratic formula here

$\Rightarrow (y + 4)^2 = 0$

$\Rightarrow y = -4$

now continue
I worked it out and got X=18...am I right?

10. Originally Posted by ENNO
I worked it out and got X=18...am I right?
no

11. Originally Posted by ENNO
I worked it out and got X=18...am I right?
You're nearly right ....... It's not 10 plus 8 .....