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## Homework Statement

My textbook does this A LOT. They divide simultaneous equations to solve. I am taking Linear Algebra right now and such a technique does not exist, then again, all of my equations are linear

Ex. [PLAIN]http://img819.imageshack.us/img819/5299/73710971.png [Broken]

Find the electric force

My book does it like this

Fx = (1) [tex]Tsin(\theta) = F_{e}[/tex]

Fy = (2) [tex]Tcos(\theta) = mg[/tex]

Divide (1) by (2) = [tex]tan(\theta) = \frac{F_{e}}{mg}[/tex]

Now I have no problem with this, I mean I can see how the mechanics, but I don't understand HOW and WHY this really works (I know this sound ridiculously hypocritical, but my literacy skills are limited). Why don't they use the old substitution method? I personally have never seen this type of method in any of my math class

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