document.write( "Question 944285: Hello,
\n" ); document.write( "How can I find \"a%5B1%5D\" and d if
\n" ); document.write( "\"+a%5B4%5D=16+\" and \"+s%5B15%5D=420++\" ?\r
\n" ); document.write( "\n" ); document.write( "I am not sure which formula to use.
\n" ); document.write( "Thanks so much.
\n" ); document.write( "

Algebra.Com's Answer #575770 by MathTherapy(10552)\"\" \"About 
You can put this solution on YOUR website!
Hello,
\n" ); document.write( "How can I find \"a%5B1%5D\" and d if
\n" ); document.write( "\"+a%5B4%5D=16+\" and \"+s%5B15%5D=420++\" ?\r
\n" ); document.write( "\n" ); document.write( "I am not sure which formula to use.
\n" ); document.write( "Thanks so much.
\n" ); document.write( "
Use the \"term\" formula to create an equation in the 2 variables, \"a%5B1%5D\" and \"d\"
\n" ); document.write( "Term formula: \"a%5Bn%5D+=+a%5B1%5D+%2B+%28n+-+1%29d\"
\n" ); document.write( "Use the \"sum of terms\" formula to create an equation in the 2 variables, \"a%5B1%5D\" and \"d\"
\n" ); document.write( "Sum of terms formula: \"S%5Bn%5D+=+%28n%2F2%29%282a%5B1%5D+%2B+%28n+-+1%29d%29\"\r
\n" ); document.write( "\n" ); document.write( "From the 2 equations just formed, solve for the 2 variables, \"a%5B1%5D\" and \"d\"\r
\n" ); document.write( "\n" ); document.write( "You should get: 1st term, or \"highlight_green%28a%5B1%5D+=+7%29\"
\n" ); document.write( "You should get: common difference, or \"highlight_green%28d+=+3%29\"
\n" ); document.write( "Then do a check!!
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\n" ); document.write( "If you need a complete and detailed solution, let me know!!
\n" ); document.write( "
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