The circle equation is .
Transform the equation into rotated form.
Substitute and in .
Therefore, the equation remains unchanged under any rotation .
The equation remains unchanged under any rotation .
![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/step1.JPG\")
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.![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=995a4339cdcc181151c427dbcf0fb0ee.png\")
and ![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=9753adde49aee6959c0a52c93ba18bc7.png\")
in .![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=f2aaaa58af28b3902bf6f0eca410b6c5.png\")
![\"\"](\"http://www.mathskey.com/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=f5eeecc5a647788163c8e35fccb82aa3.png\")
remains unchanged under any rotation ![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=401dfc03d5a8a06a3a1afbe88b95cc4f.png\")
.![\"\"](\"/userfiles/image/steps_images/solution.JPG\")
remains unchanged under any rotation ![\"\"](\"http://www.mathskey.com/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=401dfc03d5a8a06a3a1afbe88b95cc4f.png\")
.