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6.23.19  Rewriting sin, cos, tan in terms of tan(x/2): halftan

The halftan command rewrites the trigonometric functions in terms of tan(x/2) using the identities:

     
  sin(x)
2tan


x
2



tan2


x
2



+1
         
cos(x)
1−tan2


x
2



tan2


x
2



+1
         
tan(x)
2tan


x
2



1−tan2


x
2



         


Examples.


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