document.write( "Question 588275: State whether the following sequences are arithmetic; and if so, state the common difference.
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Algebra.Com's Answer #374433 by Edwin McCravy(20059)\"\" \"About 
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document.write( "15, 18, 21, 24\r\n" );
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document.write( "How to tell if it is arithmetic.\r\n" );
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document.write( "1. Subtract the 1st term from the 2nd term.  Notice what you get. 18-15 = 3\r\n" );
document.write( "2. Subtract the 2nd term from the 3rd term.  Notice what you get. 21-18 = 3\r\n" );
document.write( "3. Subtract the 3rd term from the 4th term.  Notice what you get. 24-21 = 3\r\n" );
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document.write( "Since we got the same difference 3 each time we subtracted a term from the\r\n" );
document.write( "next one, the difference 3 was in common.  So we call 3 a \"common difference\"\r\n" );
document.write( "and the sequence is an arithmetic sequence.\r\n" );
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document.write( "Edwin
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