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document.write( "The complement of an angle A is 90-A. \"Complementary angles add to 90 degrees\" \n" );
document.write( "The supplement of an angle A is 180-A. \"Supplementary angles add to 180 degrees\" \r \n" );
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document.write( "It is best to memorize this. \r \n" );
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document.write( "For the problem you posted, just replace A with \"(x+y)\" and you are done.