document.write( "Question 1125867: What is the next numbers in these sequences and why are they as they are:
\n" ); document.write( "-9 -8 -4 5 21 46 ... ...
\n" ); document.write( "and
\n" ); document.write( "2 4 6 10 16 26 42 ... ...
\n" ); document.write( "Thank you
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Algebra.Com's Answer #742195 by MathLover1(20850)\"\" \"About 
You can put this solution on YOUR website!
1.
\n" ); document.write( "\"-9\",\"+-8\",\"+-4\",\"+5\",\"+21\",\"+46\" ... ...\r
\n" ); document.write( "\n" ); document.write( "Find nth term formula using differences.\r
\n" ); document.write( "\n" ); document.write( "Differences:\r
\n" ); document.write( "\n" ); document.write( "\"-9+\"| |\"+-8\" | |\"+-4\" | |\"+5+\"| | \"21\" | | \"46\"
\n" ); document.write( "..... | \"1\" | |\"+4\" | | \"9\" | | \"16\" | |\"+25\" |
\n" ); document.write( "............ | | \"3+\"| |\"+5\" | |\"+7\" | | \"9\" | |
\n" ); document.write( "............. | | |\"+2+%7C+%7C%7B%7B%7B+2+\"| | \"2+\"| | | \r
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\n" ); document.write( "\n" ); document.write( "since we have three differences, the general form for finding the nth term in a cubic sequence is \r
\n" ); document.write( "\n" ); document.write( "\"a%5Bn%5D=an%5E3+%2B+bn%5E2+%2B+cn+%2B+d\"\r
\n" ); document.write( "\n" ); document.write( "Set up a system of four equations with four variables to find the coefficients \"a\", \"b\", \"c\" and \"d\". \r
\n" ); document.write( "\n" ); document.write( "Use the values given in the sequence as if they were points on a graph in the form (\"n\", \"nth\").
\n" ); document.write( "It is easiest to start with the first \"4\" terms, as they are usually smaller or simpler numbers to work with.\r
\n" ); document.write( "\n" ); document.write( "so, we have:
\n" ); document.write( "(\"1\", \"-9\"), (\"2\",\"+-8\"), (\"3\",\"-4\"), (\"4\",\"+5\") \r
\n" ); document.write( "\n" ); document.write( "Plug in to: \r
\n" ); document.write( "\n" ); document.write( "\"a%5Bn%5D=an%5E3+%2B+bn%5E2+%2B+cn+%2B+d\"\r
\n" ); document.write( "\n" ); document.write( "(\"1\", \"-9\")\r
\n" ); document.write( "\n" ); document.write( "\"-9=a%2A1%5E3+%2B+b%2A1%5E2+%2B+c%2A1+%2B+d\"
\n" ); document.write( "\"-9=a%2B+b+%2B+c+%2B+d\"...............eq.1\r
\n" ); document.write( "\n" ); document.write( "(\"2\",\"+-8\")\r
\n" ); document.write( "\n" ); document.write( "\"-8=a%2A2%5E3+%2B+b%2A2%5E2+%2B+c%2A2+%2B+d\"
\n" ); document.write( "\"-8=8a%2B+4b+%2B+2c+%2B+d\"...............eq.2\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "(\"3\",\"-4\")\r
\n" ); document.write( "\n" ); document.write( "\"-4=a%2A3%5E3+%2B+b%2A3%5E2+%2B+c%2A3+%2B+d\"
\n" ); document.write( "\"-4=27a%2B+9b+%2B+3c+%2B+d\"...............eq.3\r
\n" ); document.write( "\n" ); document.write( "(\"4\",\"+5\")\r
\n" ); document.write( "\n" ); document.write( "\"5=a%2A4%5E3+%2B+b%2A4%5E2+%2B+c%2A4+%2B+d\"
\n" ); document.write( "\"5=64a%2B+16b+%2B+4c+%2B+d\"...............eq.4\r
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\n" ); document.write( "\n" ); document.write( "Solve the system of \"4\" equations using your favorite method.\r
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\n" ); document.write( "\n" ); document.write( "In this example, the results are: \r
\n" ); document.write( "\n" ); document.write( "\"a+=+1%2F3\", \"b+=+-1%2F2\", \"c+=+1%2F6\", \"d+=+-9\"\r
\n" ); document.write( "\n" ); document.write( "then we have\r
\n" ); document.write( "\n" ); document.write( "\"a%5Bn%5D=%281%2F3%29n%5E3+-%281%2F2%29n%5E2+%2B+%281%2F6%29n+-9\"\r
\n" ); document.write( "\n" ); document.write( "and next term will be:\r
\n" ); document.write( "\n" ); document.write( "\"n=7\"\r
\n" ); document.write( "\n" ); document.write( "\"a%5B7%5D=%281%2F3%297%5E3+-%281%2F2%297%5E2+%2B+%281%2F6%297+-9\"\r
\n" ); document.write( "\n" ); document.write( "\"highlight%28a%5B7%5D=82%29\"\r
\n" ); document.write( "\n" ); document.write( "here are some more terms:\r
\n" ); document.write( "\n" ); document.write( "\"-9\",\"+-8\",\"+-4\",\"+5\",\"+21\",\"+46\" \"82\",\"+131\",\"+195\",\"276\",\"+376\",\"+497\".............\r
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\n" ); document.write( "\n" ); document.write( "2.\r
\n" ); document.write( "\n" ); document.write( "\"2\", \"4\", \"6\", \"10\" ,\"16\", \"26\",\"+42\", ... .\r
\n" ); document.write( "\n" ); document.write( "track the sequence of \"adding\" the previous \"2\" numbers combined:\r
\n" ); document.write( "\n" ); document.write( "\"2%2B4+=6\"\r
\n" ); document.write( "\n" ); document.write( "\"4%2B6=10\"\r
\n" ); document.write( "\n" ); document.write( "\"6%2B10=16\"\r
\n" ); document.write( "\n" ); document.write( "\"10%2B16=26\"\r
\n" ); document.write( "\n" ); document.write( "\"16%2B26=42\"\r
\n" ); document.write( "\n" ); document.write( "so, the next term will be:\r
\n" ); document.write( "\n" ); document.write( "\"26%2B42=68\"\r
\n" ); document.write( "\n" ); document.write( "your answer is:\"+68\"\r
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\n" ); document.write( "\n" ); document.write( "some more terms:\r
\n" ); document.write( "\n" ); document.write( "\"2\", \"4\", \"6\", \"10\", \"16\", \"26\",\"+42\", \"68\", \"110\", \"178\", \"288\", \"466\", \"754\", \"1220\", ...\r
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