# How to solve a linear equation by substitution?

I've been having a tough time figuring this out. This is how I wrote out the question with substitution.

\begin{align} & I_2 = I_1 + aI_1 (T_2 - T_1) \\ & I_1=100\\ &T_2=35\\ &T_1=-5\\ &a=0.000011 \end{align}

My try was $I_2 = 100(1) + 0.000011(100) (35(2)-5(1))$

The answer is $100.044$m but I can't figure out the mechanics of the question.

Thanks in advance for any help

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I tried to post a screen shot of the question, but I don't have enough points to do so. If you click on question though it will show the image. – CaviB Feb 27 '13 at 2:49
Welcome to math.SE! For the best results, try to give as much information as you think is pertinent. In this case, give your values, for instance, is $I_1=100$ correct? If you are not certain exactly how to format, do the best you can to make it (at least) human interpretable, and someone will translate it for you into LaTeX, in order that the information is best communicated to this vast and knowledgeable site! – adam W Feb 27 '13 at 2:53
@CaviB I have updated the post with LaTeX, can you please confirm that this is correct? – Jeel Shah Feb 27 '13 at 3:02
@gekkostate: I think I got it right. CaviB please confirm. – Ross Millikan Feb 27 '13 at 3:35
Yes it's correct thank you for the help. – CaviB Feb 28 '13 at 1:27

## 1 Answer

The lower temperature is $-5$ and you dropped a sign plus should not be multiplying $T_2$ by $2$. The correct calculation is $I_2=100+0.000011\cdot 100 \cdot (35-(-5))=100.044$

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Yeah I totally misunderstood the substitution (l1 = 100 not 100(1) and T2 = 35 not 35(2)). Thanks again for the guys. – CaviB Feb 28 '13 at 1:30