



There are an infinite number of trig formulas




that people could think up. 


Obviously you
can't remember them all. 





After you have worked with trig
for a while,



you will find that you have memorized some trig values.



Whether you
wanted to or not. 


Things like: 


sin
0° = 
0 

cos
0° = 
1.0 
sin
30° = 
0.5 

cos
30° = 
0.866 
sin
45° = 
0.7071 

cos
45° = 
0.7071 
sin
60° = 
0.866 

cos
60° = 
0.5 
sin
90° = 
1.0 

cos
90° = 
0 






But for most
other angles you have to use a calculator or look them up in a book. 


But what if
you didn't have a calculator or a book? What then eh? 


Well most
sane people would say: 


Then go get
one! 


Well, many
math teachers aren't most sane people. (Did that come out right?) 





Anyway, your
math teacher may want you to learn more formulas 


for finding other
angles. 





Some of these formulas do
have other uses, 


and working with them will make you more
comfortable 


working with trig stuff in general. 


But if your
teacher puts a bunch of time in on these, 


they are probably pretty
close to retirement age. 





OK, with that
as a pep talk for this page, here we go. 





Imagine you
are a Neanderthal. 


You get offended by the Geico commercial, walk
out of your cave, 


fight off a wooly mammoth, 


and decide you need to
know what the sine of 15°
is. 





You don't
remember it, but you do remember the sine of 30° 


and you also remember a formula for finding the sine of half of an
angle 


that you already know the sine for: 











Remember, I said use your
imagination. 


Imagine that you know all these formulas 


but $2 trig
calculators haven't been invented yet. 





So we know the sine of 30°
is 0.5,



so substitute into the formula and get the answer.






more
to come on this topic! 























copyright 2008 Bruce Kirkpatrick

