document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1109441>Question 1109441</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The 13th and 7th terms of an arithmetic sequence are 15 and 51 respectively <BR>\n" );
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document.write( "Which term is equal to-21?<BR>\n" );
document.write( "Show that 66 is not a term of the sequence </SPAN>\n" );
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document.write( "An arithmetic error in the beginning of the work shown by the other tutor makes the rest of her response incorrect....<br><BR>\n" );
document.write( "It is 6 more terms from the 7th to the 13th; the value changes from 51 to 15, a decrease of 36.  So the common difference is -36/6 = -6.<br><BR>\n" );
document.write( "-21 is 36 less than 15, which is the 13th term.  You could use the common difference of -6 to determine which term is -21.  However, we already know that the difference is 36 when the terms are 6 terms apart.  So the term that is -21 is term #(13+6), or term 19.<br><BR>\n" );
document.write( "The difference between 66 and 51 is 15, which is not a multiple of 6; therefore since 51 is a term of the sequence, 66 is not. </SPAN>\n" );
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