July 22nd, 2019, 03:05 AM  #1 
Member Joined: Sep 2013 Posts: 93 Thanks: 2  Rotated ellipse equation
Hello Can you tell me why is there no minus sign before (xh)*sin(A) and why is there one before (yk)*cos(A) on the accepted answer's equation here(second fraction)? https://math.stackexchange.com/quest...ginandrotate According to this site(derivation section) https://en.wikipedia.org/wiki/Rotation_of_axes it should be (xh)*sin(A) and +(yk)*cos(A) The equation is right, I just don't see why. 
July 22nd, 2019, 04:48 AM  #2 
Member Joined: Sep 2013 Posts: 93 Thanks: 2 
seems like changing + and  gives the same ellipse, so both seems to be correct

July 22nd, 2019, 08:20 AM  #3 
Senior Member Joined: Sep 2015 From: USA Posts: 2,590 Thanks: 1434 
rotate an ellipse 180 degrees and what do you get?

July 23rd, 2019, 01:30 AM  #4 
Member Joined: Sep 2013 Posts: 93 Thanks: 2  

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ellipse, equation, rotated 
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