Thread: parabola intersection

Using a graphing utility to find the point of intersection of the graphs. Then confirm your solution algebraically.
y=3x^2
y=2x^2-8x-15


I did this graphically and I got (-3,27). How do I find the solution algebraically? I know it can't be hard, but I can't find it in the book.

Originally Posted by RenSully

Using a graphing utility to find the point of intersection of the graphs. Then confirm your solution algebraically.
y=3x^2
y=2x^2-8x-15


I did this graphically and I got (-3,27). How do I find the solution algebraically? I know it can't be hard, but I can't find it in the book.

Set .

In otherwords, solve



for x.

Can I say something though ? The question is wrong. You must give different letters to different equations. What you wrote means that for any in , , which is wrong.

So I would rather denote the two parabolas like this :




Thus solve for , ... and Von Nemo already answered this I was just posting because of this (since solving for is absolutely meaningless, even though you understand it ... I mean let's talk math !)

Thanks! I wish I were studying Nietzche/philosophy instead of Pre-calc. I am never going to remember all of this. Sigh...

Originally Posted by Bacterius

... and Von Nemo already answered this I was just posting because of this (since solving for is absolutely meaningless, even though you understand it ... I mean let's talk math !)

The question - I believe - is that we are looking for .

Note that this implies that .

You are trying to distinguish between two parabolas, but notice the word "intersection". Once this word was tossed into the game, y became equal to y.

Oh right, thanks for the explanation