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- Jul 15th 2013, 10:03 AM #1

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## How was this solved?

The question asks me to determine the intersection 3x-y=11 and 3x

^{2}-y^{2 }= 47 This is the given answer.

y=3x-11

3x^{2}-(3x-11)^{2}=47

3x^{2}-9x^{2 }+66x-121-47=0

-6x^{2}+ 66x - 168= 0

x^{2 }-11x +28 = 0

..... and so on

The problem I'm having is in line 3. I'm not sure where the '66x' came from?

- Jul 15th 2013, 10:31 AM #2

- Jul 15th 2013, 11:18 AM #3

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## Re: How was this solved?

Is there anyway you can explain this step by step.

I can see that 3x squared = 9x^{2}and I see that -11 squared = 121, however I don't know where the (2 x 11 x 3)x came from :S

Also in the given answer for the question it says that instead of 121 it's -121.. im so confused.

- Jul 15th 2013, 11:56 AM #4

- Jul 15th 2013, 12:32 PM #5

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## Re: How was this solved?

Yes thank you very much, I see how it was done now, however I highly doubt I will ever be able to do it myself on a test. I had to stare at this for a while and I'm still having trouble understanding it completely.

Thank you though, I've definitely come as close to understanding it as I probably ever will.

- Jul 15th 2013, 01:40 PM #6