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MathGroup Archive 2000

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RE: A trig identity that Mathematica doesn't know?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg22242] RE: [mg22172] A trig identity that Mathematica doesn't know?
  • From: "Simons, F.H." <F.H.Simons at tue.nl>
  • Date: Sat, 19 Feb 2000 01:33:42 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Gianluca,

To show that

expr = ArcTan[ y/Sqrt[R^2-y^2] ] - ArcSin[ y/R ]

equals 0 for 0<y<R, you might compute the sine of the expression and show
that it zero:

Simplify[ TrigExpand[ Sin[expr]], R>0]

The condition R>0 is necessary!

Fred Simons
Eindhoven University of Technology



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