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# easy system of equations keeps going wrong watch

1. Hey guys,

I have the following to solve:

(12*10^5)a + (6*10^5)b + (6*10^5)c = -1000

(6*10^5)a + (4*10^5)b + (2*10^5)c = 0

(6*10^5)a + (2*10^5)b + (8*10^5)c = 500

I keep solving by using the first equation to get a as the subject, then sub that in to 2 and make b the subject then finally sub all in to 3 to solve.

The answers (rounded) should be a=-0.0058, b=0.0075 and c=0.0025

Can anyone help as I keep getting:

b=0.00875 and c=0.00375

thanks
2. How about: Add the second to the third, then subtract the first to eliminate 'a' and 'b' at the same time...
3. yeh that is easier.

Am I doing something wrong though because I am still getting 0.00375 instead of 0.0025?
4. (Original post by Big_Sam)
yeh that is easier.

Am I doing something wrong though because I am still getting 0.00375 instead of 0.0025?
I agree with you: c = 0.00375.
5. yeh but its a past exam paper and the answers should be the ones in the op
6. (Original post by Big_Sam)
yeh but its a past exam paper and the answers should be the ones in the op
Well then either the equations you've got have a mistake in them/are different to the ones in the actual paper, or the answers are wrong...

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