document.write( "Question 1165103: My question is how do I arrive at the books answer?\r
\n" ); document.write( "\n" ); document.write( "Book says, “Determine the appropriate rotation formula to use so that the new equation contains no xy-term.”
\n" ); document.write( "25x^2-36xy+40y^2-12sqrt(13)x-8sqrt(13)y=0
\n" ); document.write( "Answers in the back of the book say x=sqrt(13)/13(3x’-2y’) and y=sqrt(13)/13(2x’+3y’)
\n" ); document.write( "The angle I get is cot(2theta)=5/13 so cos(2theta)=5/sqrt(194) which doesn’t lead to the books answer. \n" ); document.write( "

Algebra.Com's Answer #789575 by Edwin McCravy(20056) $\"\"$ $\"About$

You can put this solution on YOUR website!

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document.write( "The angle of rotation θ is given by\r\n" );
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document.write( "You have 5/13, not 5/12.  Try it with that.  Everything should come out a lots\r\n" );
document.write( "nicer.  If you still have trouble let me know in the space below and I'll\r\n" );
document.write( "get back to you by email.\r\n" );
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document.write( "Also, remember, there are two angles that will eliminate the xy term. The\r\n" );
document.write( "back of the book may use the other one from the one you use.\r\n" );
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document.write( "Edwin

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