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July 24th, 2009, 04:55 PM   #1
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help with problem

the problem is this
solve this problem by completing the square

Code:
2x^2-12x+11
I keep getting 2(x-3)^2+11

they (the book) says the answer is

2(x-3)^2-7


could anyone offer a quick step by step so i can see where I am wrong or where they are wrong?
thanks
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July 24th, 2009, 05:58 PM   #2
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Re: help with problem

Expand algebraically, then this obviously tells you the reason.
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July 24th, 2009, 06:04 PM   #3
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Re: help with problem

ya, no duh, but if i don't know the answer, how do i find it? what I am saying is this, I move the 11 over to the other side complete the square and end up with 2(x-3)^2 = -11 then i move the 11 back over and have 2(x-3)^2 + 11 and if i expand the problem then I have 2(x^2 -6x +9) + 11 which then becomes 2x^2 -12x +18 + 11 which becomes 2x^2 - 12x + 29 good luck factoring that am I saying 2x^2 - 12x +36 - 7 ??? i am getting lost here
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July 24th, 2009, 06:07 PM   #4
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Re: help with problem

Be smart. Do what I tell you, and you will logically understand the meaning of my words.
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July 24th, 2009, 06:12 PM   #5
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Re: help with problem

Sigh.

Expanding the thing will become , and this is what you've got for part of your answer, which was wrong. But, this obviously tells you how to solve it now.
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July 24th, 2009, 06:13 PM   #6
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Re: help with problem

I did that before I posted the question...
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July 24th, 2009, 06:14 PM   #7
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Re: help with problem

I hope they've taught you subtraction back in the school days.
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July 24th, 2009, 06:15 PM   #8
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Re: help with problem

if i am not given the answer, how do i work it forwards............
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July 24th, 2009, 06:20 PM   #9
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Re: help with problem

Quote:
Originally Posted by SteveThePirate
if i am not given the answer, how do i work it forwards............ tell me that or stop posting you arrogant guy(cant curse for fear of being banned)
This problem is not hard, as long you follow what I say dude, calm down pirate! LET ME CLARIFY.

The problem asks to CTS in order to find the values for when the equation equals to . Let , where is our value we are looking for. Expand the expression, and we will get . , so the will tell ya what you need. , and so on.
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July 24th, 2009, 06:26 PM   #10
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Re: help with problem

that does make sense to me but my big problem is that, the answer is not a given, so you do not know that it will be - 7 at the end, and I realized how to get the answer once i had the answer, but, is there always going to be a ( + k at the end of a factor problem? how would i choose it to be -7 if i do not know that it is supposed to be -7?
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