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Q&A #193


Trigonometry Ratios

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From: Claudia (for Teacher2Teacher Service)
Date: Apr 27, 1998 at 20:23:37
Subject: Re: Trigonometry Ratios

The trig ratios are essentially names that have been assigned to the common 
ratios 
of similar triangles (those whose angles have the same measures, like 30-60-
90 
degrees, or any other combination whose total is 180 degrees).

There is a great fictional story written about Sohcahtoa.  Sohcahtoa is one 
way 
students can remember how to find the ratios. 

   Soh stands for Sine is Opposite over Hypotenuse 
   cah = Cosine is Adjacent over Hypotenuse
   toa = Tangent is Opposite over Adjacent.  

I prefer this mnemonic to Oscar Had A Heap Of Apples because although the 
oh..ah..oa is there, the students forget which one goes with which trig 
function.

Opposite refers to the side opposite the angle you are working with.
If I had a triangle   A

                      B    C   then  AC would be the hypotenuse because it is 
opposite the right angle of B. 

The sin A = BC/AC  since side BC is opposite angle A.  
cos A = AB/AC since AB is the side adjacent (near/connected to) angle A.

Hope this gets you started!

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