My Math Forum System of Equations help

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 July 16th, 2014, 10:26 PM #1 Newbie   Joined: Jun 2011 Posts: 8 Thanks: 0 System of Equations help Ok so I've been trying to work through this question for an hour and I just can't figure it out. I have the answer key but iut won't show me how to get the answer. ax + 5y = 10 6x + 2y = 7 The answer key says "a" should be 15 if I did it right. I can get as far as this: 2ax - 30x = -15 After that I just can't manipulate it to get an answer out of it, it's driving me nuts lol. Any help would be appreciated. EDIT: Actually apparently I just read the question closer and it says in a scenario where there is NO solution for the system "a" would equal 15. Still not sure how to work it out lol. Wait, I'm starting to piece it together, no solutions means a parallel line. I think I can solve it now. Yeah, I just decided "a" actually = 0.6, plugging in that value instead of "a" made me find some pretty obscure long decimal values for x and y, but when I actually took time to write down those exact values and plug them into any of the equations, they are correct. This question was BS. Last edited by Regnes; July 16th, 2014 at 11:01 PM.
July 17th, 2014, 09:42 AM   #2
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 Originally Posted by Regnes ax + 5y = 10 [1] 6x + 2y = 7 [2] The answer key says "a" should be 15 if I did it right. This question was BS.
[1]: y = (-a/5)x + 2
[2]: y = (-3)x + 7/2

If same slope: -a/5 = -3
a = 15
That's what you did, right?

BS = By Subtracting or By Summing?

July 19th, 2014, 10:33 PM   #3
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Quote:
 Originally Posted by Denis [1]: y = (-a/5)x + 2 [2]: y = (-3)x + 7/2 If same slope: -a/5 = -3 a = 15 That's what you did, right? BS = By Subtracting or By Summing?
Hmmm, you're right, not sure how I missed that, I was really tired when I was working through it all lol. Luckily I had my wits about me when writing the test haha.

Blah, just realized I divided both sides by 5 to eliminate the fraction, what was I thinking?

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