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Q&A #7470

Teachers' Lounge Discussion: System of equations

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From: Loyd <loydlin@aol.com>
To: Teacher2Teacher Public Discussion
Date: 2002102607:26:48
Subject: Re: Re: math system of equations

On 2002102607:25:12, N.Goodluck Nwaerondu wrote:
>On 2002102112:56:59, megan wrote:
>>	please help me solve this system of equations.
>>y=3/5x-2
>>y=x/10+1
>>y=y
>therefore: 3/5x-2=x/11  OR did you mean x/10x+1
>then cross multiply:
>3(10x+1) = x(5x-2)      OR 3(11) = x(5x-2)
>5x^2-32x-3 = 0             5x^2-2x-33=0
>Then use the quadratic formula to solve:

N.Goodluck I think the poster (who didn't use grouping symbols) meant
the following:

y=(3/5)x-2  
y=(x/10)+1    

That is, the x in eq 1 is in the numerator and the 10 in equation 2 is
in the denominator.  I often see these confusions which grouping
symbols would clear up. 

I think it is clearer if it was written using the three line method
vice the one line typewriter method:
 
y = 3x   -2
    ---
     5

y = x  + 1
    --
    10


These are equations in the y=mx+b format where the slope is 3/5 in the
first one and 1/10 in the second one.  

That is why, I recommend using grouping symbols to avoid confusion.
When using a pencil, most students and teachers get it right.  


3x -2 = x  + 1
--      --
 5      10
Multiply through by 10:

6x - 20 = x + 10

5x = 30
x =6
By substitution, we find that y = 1.6 or 8/5.



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