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
15-10=5 10/5=2 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. 15-10=5 10/5=2 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 don´t I would like an example and reasoning why it dont work.