April 9th, 2018, 05:10 AM  #1 
Member Joined: Jan 2016 From: Uk Posts: 80 Thanks: 2  ARCTAN Equation distilled
Hi, I've been given an equation for use in a project. The system has limitations, e,g, it doesn't support '^' Here is the equation: arctn= x/y/( 1+0.28125*( x/y )^2)*180/pi Firstly does it look ok as an approximation of ARCTAN? Second, is it possible to remove all brackets to show me the sequence of events, please? Camerart Last edited by skipjack; April 9th, 2018 at 06:38 AM. 
April 9th, 2018, 06:39 AM  #2 
Global Moderator Joined: Dec 2006 Posts: 18,961 Thanks: 1605 
What is the argument of arctan?

April 9th, 2018, 08:40 AM  #3 
Member Joined: Jan 2016 From: Uk Posts: 80 Thanks: 2  
April 9th, 2018, 04:54 PM  #4 
Global Moderator Joined: Dec 2006 Posts: 18,961 Thanks: 1605 
If x/y = 1, what value should the arctan have and what does the formula give? Now try another value for x/y, such as 0.5.

April 10th, 2018, 12:37 AM  #5  
Member Joined: Jan 2016 From: Uk Posts: 80 Thanks: 2  Quote:
Someone on a programming forum, has done this for me as I'm a bit of a dunce when it comes to maths and trigonometry, but to add to my confusion, I think he reversed X and Y. I actually only want to see the equation distilled to without brackets, if possible, so I can work out how it works. C.  
April 10th, 2018, 06:56 AM  #6 
Global Moderator Joined: Dec 2006 Posts: 18,961 Thanks: 1605 
arctan(u) = u/(1 + 0.28125u²) is a reasonable approximation for u < 1. So is arctan(u) = u/(1 + 0.282u²). The above both give a result in radians, so multiplying by 180$^\circ$/pi gives the value in degrees. 
April 10th, 2018, 09:13 AM  #7  
Member Joined: Jan 2016 From: Uk Posts: 80 Thanks: 2  Quote:
The original equation is working, but I'll try your neater version tomorrow, thanks. C.  

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