James...GREAT question...the BEST answer is BECAUSE!!!
Well...that is just a small protion to the answer. Long ago when
Pythagorus and other mathematicians were thinking about how math
influences our world...there were not such things as degrees,
inches, sin, cos, tan, or other units. Lucklily, someone ask how
do we know this is a right triangle, why does this line/segment
equal another, what makes these angles equal one another or if I
do this, and get two angles, how do I know they are equal. Good
thing they did it then, otherwise it would be up to us to figure
that out...but who's got time for that...I want to play on my
PS3. Anyway...mathematicians, by trial and error, began to form
rules to prove that what they said was valid...not just true,
but that by following the rule, one math guy could show(prove)
to another math guy that for every rule, it could be reproduced,
thus become valid. this was because every one, well, almost
everyone wants PROOF that this statement is true..er..valid.
Obviously, throug