Trigonometry/More About Addition Formulas

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Related FormulaeEdit

 
 
 

Tangent FormulaeEdit

 
 
 
 

In the last row of expressions, if   then the trigonometric functions are all positive so the positive sign is needed before the square root.

DerivationsEdit

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Using cofunctions we know that   . Use the formula for   and cofunctions we can write

   
 
 
 


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Having derived   we replace   with   and use the fact that cosine is even and sine is odd.

   
 
 

Related FormulaeEdit

 
 
 

DerivationsEdit

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Using   and the fact that cosine is even and sine is odd, we have