My Math Forum Rotated ellipse equation

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 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 (x-h)*sin(A) and why is there one before (y-k)*cos(A) on the accepted answer's equation here(second fraction)? https://math.stackexchange.com/quest...gin-and-rotate According to this site(derivation section) https://en.wikipedia.org/wiki/Rotation_of_axes it should be -(x-h)*sin(A) and +(y-k)*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? Thanks from ricsi046
July 23rd, 2019, 01:30 AM   #4
Member

Joined: Sep 2013

Posts: 93
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Quote:
 Originally Posted by romsek rotate an ellipse 180 degrees and what do you get?
the same

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