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November 28th, 2009, 02:15 PM   #1
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where do i start ?.....

I have the answers but i have no idea where to begin
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 November 28th, 2009, 02:24 PM #2 Member   Joined: Nov 2009 Posts: 49 Thanks: 0 Re: where do i start ?..... This is to be done without calculator
 November 28th, 2009, 03:10 PM #3 Newbie   Joined: Oct 2009 Posts: 6 Thanks: 0 Re: where do i start ?..... The answers is a=2, b=-1 and c=7?
 November 28th, 2009, 03:13 PM #4 Member   Joined: Nov 2009 Posts: 49 Thanks: 0 Re: where do i start ?..... the question is where do i start and how do i do it, but those answers are correct
 November 28th, 2009, 03:20 PM #5 Newbie   Joined: Oct 2009 Posts: 6 Thanks: 0 Re: where do i start ?..... Solve everything with systems of equations: 2a-3b=7 3a+b=7
 November 28th, 2009, 03:22 PM #6 Member   Joined: Nov 2009 Posts: 49 Thanks: 0 Re: where do i start ?..... i dont understand, what happened to the x's and where do those 7 come from
 November 28th, 2009, 03:24 PM #7 Newbie   Joined: Oct 2009 Posts: 6 Thanks: 0 Re: where do i start ?..... Sorry, I was wrong. 2a-3b=7 3a+b=5 c=7 Look to the two equations.
 November 28th, 2009, 05:42 PM #8 Global Moderator   Joined: Dec 2006 Posts: 20,826 Thanks: 2160 The question should have been "If (2a - 3b)x² + (3a + b)x + c ?7x² + 5x + 7, find the values of a, b and c." For that to be an identity, the two polynomials must be essentially the same.
 November 28th, 2009, 07:04 PM #9 Newbie   Joined: Oct 2009 Posts: 6 Thanks: 0 Re: where do i start ?..... Yes... Is this....
November 28th, 2009, 08:50 PM   #10
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Re: where do i start ?.....

Quote:
 Originally Posted by peterle1 i dont understand, what happened to the x's and where do those 7 come from
Peter,
Two polynomials are equal only if each term is the same. "term" is actually an important vocabulary word, by the way.
Another way to think of it is to match the "coefficients".

The coefficients on the left are
(2a - 3b)
(3a + b) and
c,
And these should equal 7, 5, and 7 respectively (the coefficients from the right).
That's where you get the equations
2a-3b=7
3a+b=5 and
c =7
The first two equations can be solved using the elimination or substitution method.

p.s. as some post-lobotomy joker might mention, using matrices is possible, but I'm guessing that's beyond the scope of your current studies.

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