Services & ResourcesWolfram ForumsMathGroup Archive

[Date Index] [Thread Index] [Author Index]

Re: Simplifying certain trigonometric expressions

• To: mathgroup at smc.vnet.net
• Subject: [mg121041] Re: Simplifying certain trigonometric expressions
• From: Heike Gramberg <heike.gramberg at gmail.com>
• Date: Wed, 24 Aug 2011 07:50:26 -0400 (EDT)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <201108240714.DAA11359@smc.vnet.net>

have you tried TrigExpand?

TrigExpand[Cos[2 ArcTan[y/x]]] // Simplify

ouput:

(x^2 - y^2)/(x^2 + y^2)

Heike

On 24 Aug 2011, at 09:14, SamTakoy wrote:

> Hi,
> 
> My Mathematica has no problem with
> 
> Assuming[x > 0 && y > 0, Cos[ArcTan[y/x]] // FullSimplify]
> 
> yielding x/Sqrt[x^2 + y^2], but can't do anything with
> 
> Assuming[x > 0 && y > 0, Cos[2 ArcTan[y/x]] // FullSimplify].
> 
> How does one overcome this?
> 
> Thanks,
> 
> Pavel
> 

• References:
  • Simplifying certain trigonometric expressions
    • From: SamTakoy <pavelgrinfeld@gmail.com>