document.write( "Question 1178152: Consider each given sequence start. i) Classify each as arithmetic, geometric, and/or none of these. ii) Find the 28th term. iii) Find the sum of the first 7 terms, call it S7 .
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\n" ); document.write( "a) 44, −6, 44, −4,
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Algebra.Com's Answer #807325 by MathLover1(20850)\"\" \"About 
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\"44\",\"-6\", \"44\", \"-4\",...\r
\n" ); document.write( "\n" ); document.write( "1st term \"a%5B1%5D=44\"
\n" ); document.write( "2nd term \"a%5B2%5D=-6=44-50\"
\n" ); document.write( "3rd term \"a%5B3%5D=-4=44-48\"\r
\n" ); document.write( "\n" ); document.write( "=> no common difference is \"d\"
\n" ); document.write( "\"r=-4%2F44=-1%2F11\"
\n" ); document.write( "\"r=44%2F-6=-22%2F3\"
\n" ); document.write( "=> no common ratio \"r\" \r
\n" ); document.write( "\n" ); document.write( "i) Classify each as arithmetic, geometric, and/or none of these. \r
\n" ); document.write( "\n" ); document.write( "=> no common difference \"d\", no common ratio \"r\"\r
\n" ); document.write( "\n" ); document.write( "so, the sequence is neither arithmetic nor geometric\r
\n" ); document.write( "\n" ); document.write( "to find \"n\"th term formula use differences:\r
\n" ); document.write( "\n" ); document.write( "\"44\"........\"-6\"........\"44\"........\"-4\"
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\n" ); document.write( "................\"50\"..................\"50\".....................\"48\"..................\r
\n" ); document.write( "\n" ); document.write( ".............................\"0\"..................\"2\"..................\r
\n" ); document.write( "\n" ); document.write( "....................................\"2\"..................=>\"3\"rd difference, so \"n\"th term formula
\n" ); document.write( " will be \"3\"rd degree function\r
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\n" ); document.write( "\n" ); document.write( "\"a%5Bn%5D=an%5E3%2Bbn%5E2%2Bcn%2Bd\"\r
\n" ); document.write( "\n" ); document.write( " plug in some of the values from the sequence, and then solving the resulting system of equations\r
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\n" ); document.write( "\n" ); document.write( "\"a%5Bn%5D=an%5E3%2Bbn%5E2%2Bcn%2Bd\".......\"44\"->first term, so \"n=1\"\r
\n" ); document.write( "\n" ); document.write( "\"44=a%2A1%5E3%2Bb%2A1%5E2%2Bc%2A1%2Bd\"
\n" ); document.write( "\"44=a%2Bb%2Bc%2Bd\"........eq.1\r
\n" ); document.write( "\n" ); document.write( "\"a%5Bn%5D=an%5E3%2Bbn%5E2%2Bcn%2Bd\".......\"-6\"->first term, so \"n=2\"\r
\n" ); document.write( "\n" ); document.write( "\"-6=a%2A2%5E3%2Bb%2A2%5E2%2Bc%2A2%2Bd\"
\n" ); document.write( "\"-6=8a%2B4b%2B2c%2Bd\"............eq.2\r
\n" ); document.write( "\n" ); document.write( "\"44=a%2A3%5E3%2Bb%2A3%5E2%2Bc%2A3%2Bd\"
\n" ); document.write( "\"44=27a%2B9b%2B3c%2Bd\"........eq.3\r
\n" ); document.write( "\n" ); document.write( "\"-4=a%2A4%5E3%2Bb%2A4%5E2%2Bc%2A4%2Bd\"
\n" ); document.write( "\"-4=64a%2B16b%2B4c%2Bd\"............eq.4\r
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\n" ); document.write( "\n" ); document.write( "subtract eq.1 from eq.2
\n" ); document.write( "\"-6-44=+8a%2B4b%2B2c%2Bd+-%28a%2Bb%2Bc%2Bd%29\"
\n" ); document.write( "\"-50=+8a%2B4b%2B2c%2Bd+-a-b-c-d%29\"
\n" ); document.write( "\"-50=+7a%2B3b%2Bc\".............eq.3\r
\n" ); document.write( "\n" ); document.write( "subtract eq.1 from eq.3 (reason: next term is \"44\" again)\r
\n" ); document.write( "\n" ); document.write( "\"44-44=+27a%2B9b%2B3c%2Bd-%28a%2Bb%2Bc%2Bd%29\"
\n" ); document.write( "\"0=+27a%2B9b%2B3c%2Bd-a-b-c-d\"
\n" ); document.write( "\"0=+26a%2B8b%2B2c\".......solve for \"b\"
\n" ); document.write( "\"-26a-2c=8b\"
\n" ); document.write( "\"b=-26a%2F8-2c%2F8\"\r
\n" ); document.write( "\n" ); document.write( "\"b=-13a%2F4-c%2F4\".............eq.4\r
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\n" ); document.write( "\n" ); document.write( "go to\r
\n" ); document.write( "\n" ); document.write( "\"-50=+7a%2B3%28-13a%2F4-c%2F4%29%2Bc\"........eq.3...., substitute \"b\"
\n" ); document.write( "\"-50=+c%2F4+-+%2811a%29%2F4\"......solve for \"c\"
\n" ); document.write( "\"-50%2B%2811a%29%2F4=c%2F4\"
\n" ); document.write( "\"-200%2B11a=c\".......................eq.5\r
\n" ); document.write( "\n" ); document.write( "go to\r
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\n" ); document.write( "\n" ); document.write( "\"b=-13a%2F4-c%2F4\".............eq.4, substitute \"c\"
\n" ); document.write( "\"b=-13a%2F4-%28-200%2B11a%29%2F4\"
\n" ); document.write( "\"b=50+-+6a\".................eq.6\r
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\n" ); document.write( "\n" ); document.write( "subtract eq.1 from eq.4\r
\n" ); document.write( "\n" ); document.write( "\"-4-44=64a%2B16b%2B4c%2Bd-%28a%2Bb%2Bc%2Bd%29\"............substitute \"b\" from eq.6 and \"c\" from eq.5\r
\n" ); document.write( "\n" ); document.write( "\"-4-44=64a%2B16b%2B4c%2Bd-a-b-c-d\"
\n" ); document.write( "\"-48=63a%2B15b%2B3c+\"
\n" ); document.write( "\"-48=63a%2B15%2850+-+6a%29%2B3%28-200%2B11a%29+\"
\n" ); document.write( "\"-48=63a%2B750+-+90a-600%2B33a+\" ....solve for \"a\"
\n" ); document.write( "\"-48=6a%2B150\"
\n" ); document.write( "\"6a=-48-150\"
\n" ); document.write( "\"6a=-198\"
\n" ); document.write( "\"a=-33\"\r
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\n" ); document.write( "\n" ); document.write( "go to
\n" ); document.write( "\"b=50+-+6a\".................substitute \"a\"
\n" ); document.write( "\"b=50+-+6%28-33%29\"
\n" ); document.write( "\"b=50+%2B+198\"
\n" ); document.write( "\"b=248\"\r
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\n" ); document.write( "\n" ); document.write( "go to\r
\n" ); document.write( "\n" ); document.write( "\"-200%2B11a=c\"........................substitute \"a\"\r
\n" ); document.write( "\n" ); document.write( "\"-200%2B11%28-33%29=c\"
\n" ); document.write( "\"-200-363=c\"
\n" ); document.write( "\"c=-563\"\r
\n" ); document.write( "\n" ); document.write( "go to
\n" ); document.write( "\"44=a%2Bb%2Bc%2Bd\"........eq.1substitute \"a\",\"b\", and \"c\"\r
\n" ); document.write( "\n" ); document.write( "\"44=-33%2B248-563%2Bd\"
\n" ); document.write( "\"44=-348%2Bd\"
\n" ); document.write( "\"44%2B348=d\"
\n" ); document.write( "\"d=392\"\r
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\n" ); document.write( "\n" ); document.write( "so, coefficients are:\r
\n" ); document.write( "\n" ); document.write( "\"a+=+-33\", \"b+=+248\", \"c+=+-563\", \"d+=+392\"\r
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\n" ); document.write( "\n" ); document.write( "and equation is:\r
\n" ); document.write( "\n" ); document.write( "\"a%5Bn%5D=-33n%5E3%2B248n%5E2-563n%2B392\"\r
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\n" ); document.write( "\n" ); document.write( "ii) Find the \"28\"th term. \r
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\n" ); document.write( "\n" ); document.write( "\"a%5B28%5D=-33%2A28%5E3%2B248%2A28%5E2-563%2A28%2B392\"
\n" ); document.write( "\"a%5B28%5D=-545356\"\r
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\n" ); document.write( "\n" ); document.write( "iii) Find the sum of the first \"7+\"terms, call it \"S7\" .
\n" ); document.write( "we have \"44\",\"-6\", \"44\", \"-4\",...\r
\n" ); document.write( "\n" ); document.write( "first find \"5\"th, \"6\"th, and \"7\"th term\r
\n" ); document.write( "\n" ); document.write( "\"a%5B5%5D=-33%2A5%5E3%2B248%2A5%5E2-563%2A5%2B392=-348\"
\n" ); document.write( "\"a%5B6%5D=-33%2A6%5E3%2B248%2A6%5E2-563%2A6%2B392=-1186\"
\n" ); document.write( "\"a%5B7%5D=-33%2A7%5E3%2B248%2A7%5E2-563%2A7%2B392=-2716\"\r
\n" ); document.write( "\n" ); document.write( "\"44\",\"-6\", \"44\", \"-4\",\"-348\",\"-2716\",\"-2716\"\r
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\n" ); document.write( "\n" ); document.write( "the sum is \"S%5B7%5D=44-6%2B44-4-348-2716-2716+=-5702\"\r
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