Date: May 28, 2013 11:43 AM
Author: Michael
Subject: Name this formula

Today our teacher showed us a way to solve problems like this:            
Theres a triangle with the base of 20cm and a line horizontal in the triangle that's 15cm. The line about the horzontal line is 8cm and the other one is X. Find x

Trying to explain this as good as i can but basicly its a triangle ABCDEF clockwise and theres a horisontal line between B and E (10 cm).
Then B->C=8cm and A->B=X
Finally the base (E->A) was 15cm.

(Hope most people get it)

He showed a way that almost took him up to 20 minutes to explain but i was thinking about this

That means 8 is 2 times bigger then X
so 8/2=4=x

I also found it work if we only knew the bottom one by changing it a little like this.
2x8=X=16 (simply changing the "divide by 2" into "multiply by 2")

But he said that I couldent use it unless i could prove it .
So is there allready a formula like this one or any way to prove it works? If it donĀ“t I would like an example and reasoning why it dont work.