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 September 6th, 2012, 12:51 PM #1 Newbie   Joined: Sep 2012 Posts: 4 Thanks: 0 Alg help, multi variable I got a couple multi variable equations I'm stuck on, I can't figure out what I'm doing wrong. One of them that's not multi variable is 19t- (2(t-1)/19) = 20 solve for T, I got 382/359 but it comes out to equal 20.2 something. Another one is u(v-+w(v-4)=z(v-1), help please.
 September 6th, 2012, 12:56 PM #2 Senior Member   Joined: Feb 2012 Posts: 628 Thanks: 1 Re: Alg help, multi variable For the second equation, assuming u, w, and z are constants, then we simply solve for v: $u(v - 8 ) + w(v - 4)= z(v - 1)$ $uv - 8u + wv - 4w= zv - z$ $uv + wv - zv= 8u + 4w - z$ $v(u + w - z)= 8u + 4w - z$ $v= \frac{8u + 4w - z}{u + w - z}$ There are infinitely many solutions in all four variables: just pick values for u, w, and z such that $u + w - z \neq 0$ and then calculate the value for v using the above equation.
 September 6th, 2012, 12:59 PM #3 Global Moderator   Joined: May 2007 Posts: 6,834 Thanks: 733 Re: Alg help, multi variable Show your work for the first problem.
 September 6th, 2012, 01:03 PM #4 Senior Member     Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 521 Math Focus: Calculus/ODEs Re: Alg help, multi variable For the first problem: $19t-\frac{2(t-1)}{19}=20$ Multiply through by 19: $361t-2(t-1)=380$ $361t-2t+2=380$ $359t=378$ $t=\frac{378}{359}$ For the second problem, there will not necessarily be a unique solution, you may solve for one variable in terms of the other three.
September 6th, 2012, 01:15 PM   #5
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Re: Alg help, multi variable

Quote:
 Originally Posted by MarkFL For the first problem: $19t-\frac{2(t-1)}{19}=20$ Multiply through by 19: $361t-2(t-1)=380$ $361t-2t+2=380$ $359t=378$ $t=\frac{378}{359}$ For the second problem, there will not necessarily be a unique solution, you may solve for one variable in terms of the other three.
How did you get 20.2?

 September 6th, 2012, 01:57 PM #6 Newbie   Joined: Sep 2012 Posts: 4 Thanks: 0 Re: Alg help, multi variable I typed the wrong problem, it was v+8, but I redid the problem exactly as you showed and my online homework thing said it was wrong. I double checked it and everything, I'll have to ask the teacher tomorrow. I got one more problem that I want to make sure I got right, At-b/c-b(1-5t) = 9 at-b/c-b+5bt=9 At-B= 9(c-b+5tb) At-B=9c-9b+45Bt At-45Bt=9c-8B t(A-45B)=9c-8B t=9C-8B/A-45B Is that correct?
 September 7th, 2012, 12:42 PM #7 Global Moderator   Joined: May 2007 Posts: 6,834 Thanks: 733 Re: Alg help, multi variable Be careful with using paraentheses. For example the last line should read t=(9C-8B)/(A-45B). Without the parentheses it looks wrong. Going from the first to the second line looks like also missing parentheses.

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