# Thread: substitute in x co ordinates to find y co ordiantes

1. ## substitute in x co ordinates to find y co ordiantes

i did all the working for this - the points of intersection for y=3x^2+5x-6 and y=-2x^2-3x+18 is when both eqations are same = 5x^2+8x-24 i found the two x valuesx1=1.532 and x2=-3.132 now i have to sub x co ordiantes to get the matching 2 y values.. ummm which formula do i sub it into and how? acan anyone help please

2. ## Re: substitute in x co ordinates to find y co ordiantes

Originally Posted by studenthelp10
i did all the working for this - the points of intersection for y=3x^2+5x-6 and y=-2x^2-3x+18 is when both eqations are same = 5x^2+8x-24 i found the two x valuesx1=1.532 and x2=-3.132 now i have to sub x co ordiantes to get the matching 2 y values.. ummm which formula do i sub it into and how? acan anyone help please
$\begin{cases}y_1=3x^2_1+5x_1-6 \\y_2=3x^2_2+5x_2-6\end{cases}$

or :

$\begin{cases}y_1=-2x^2_1-3x_1+18 \\y_2=-2x^2_2-3x_2+18\end{cases}$

3. ## Re: substitute in x co ordinates to find y co ordiantes

You have just found 2 x values for which the two equations for y are equal so can sub in either. You could of course check that your x values are correct by substituting in both and getting the same answers.

4. ## Re: substitute in x co ordinates to find y co ordiantes

okay thanks ill try now

5. ## Re: substitute in x co ordinates to find y co ordiantes

yup i got the right answer ! it matches the graphical points of the calculators thanks !