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July 22nd, 2019, 03:05 AM   #1
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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.
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July 22nd, 2019, 04:48 AM   #2
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seems like changing + and - gives the same ellipse, so both seems to be correct
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July 22nd, 2019, 08:20 AM   #3
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rotate an ellipse 180 degrees and what do you get?
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July 23rd, 2019, 01:30 AM   #4
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Quote:
Originally Posted by romsek View Post
rotate an ellipse 180 degrees and what do you get?
the same
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