document.write( "Question 988607: The fourth term of a geometric progression exceeds the third term by 54, and the sum of the second and third term is 36. Find the common ratio if it is positive \n" ); document.write( "
Algebra.Com's Answer #609118 by MathLover1(20850)\"\" \"About 
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if the fourth term \"a%5B4%5D\" exceeds the third term \"a%5B3%5D\" by \"54\", we have\r
\n" ); document.write( "\n" ); document.write( "\"a%5B4%5D-a%5B3%5D+=54\"....eq.1\r
\n" ); document.write( "\n" ); document.write( " if the sum of the second \"a%5B2%5D\"and third term \"a%5B3%5D\" is \"36\", we have\r
\n" ); document.write( "\n" ); document.write( "\"a%5B2%5D%2Ba%5B3%5D=36\"....eq.2\r
\n" ); document.write( "\n" ); document.write( "By using \"a%5Bn%5D=a%5B1%5D%2Ar%5E%28n-1%29\" we have:\r
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\n" ); document.write( "\n" ); document.write( "\"a%5B1%5D%2Ar%5E3-a%5B1%5D%2Ar%5E2=54\"....eq.1\r
\n" ); document.write( "\n" ); document.write( "\"a%5B1%5D%2Ar%2Ba%5B1%5D%2Ar%5E2=36\"....eq.2
\n" ); document.write( "---------------------------------------------------add eq.2 and eq.1\r
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\n" ); document.write( "\n" ); document.write( "\"a%5B1%5D%2Ar%5E3-a%5B1%5D%2Ar%5E2%2Ba%5B1%5D%2Ar%2Ba%5B1%5D%2Ar%5E2=54%2B36\"\r
\n" ); document.write( "\n" ); document.write( "\"a%5B1%5D%2Ar%5E3%2Ba%5B1%5D%2Ar=90\"\r
\n" ); document.write( "\n" ); document.write( "\"a%5B1%5D%28r%5E3%2Br%29=90\"\r
\n" ); document.write( "\n" ); document.write( "\"a%5B1%5D=90%2F%28r%5E3%2Br%29\".............substitute in eq.2\r
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\n" ); document.write( "\n" ); document.write( "\"90%2F%28r%5E3%2Br%29%2Ar%2B90%2F%28r%5E3%2Br%29%2Ar%5E2=36\"....eq.2\r
\n" ); document.write( "\n" ); document.write( "\"90r%2F%28r%5E3%2Br%29%2B90r%5E2%2F%28r%5E3%2Br%29=36\"\r
\n" ); document.write( "\n" ); document.write( "\"%2890r%2B190r%5E2%29=36%28r%5E3%2Br%29\"\r
\n" ); document.write( "\n" ); document.write( "\"90r%281%2Br%29=36r%28r%5E2%2B1%29\"......divide by \"18\"\r
\n" ); document.write( "\n" ); document.write( "\"5%281%2Br%29=2%28r%5E2%2B1%29\"\r
\n" ); document.write( "\n" ); document.write( "\"5%2B5r=2r%5E2%2B2\"\r
\n" ); document.write( "\n" ); document.write( "\"2r%5E2%2B2-5r-5=0\"\r
\n" ); document.write( "\n" ); document.write( "\"2r%5E2-5r-3=0\"\r
\n" ); document.write( "\n" ); document.write( "\"%28r-3%29+%282+r%2B1%29+=+0\"\r
\n" ); document.write( "\n" ); document.write( "=> one solution will be: \"%28r-3%29+=+0\"=> \"highlight%28r=3%29\"
\n" ); document.write( "=> another solution will be: \"2r%2B1=0\"=>\"2r=-1\"=>\"highlight%28r=-1%2F2%29\"\r
\n" ); document.write( "\n" ); document.write( "now we can find first term:\r
\n" ); document.write( "\n" ); document.write( "if \"highlight%28r=3%29\"\r
\n" ); document.write( "\n" ); document.write( "\"a%5B1%5D%2A%283%29%2Ba%5B1%5D%2A%283%29%5E2=36\"....eq.2\r
\n" ); document.write( "\n" ); document.write( "\"3a%5B1%5D%2B9a%5B1%5D=36\"
\n" ); document.write( "\"12a%5B1%5D=36\"
\n" ); document.write( "\"highlight%28a%5B1%5D=3%29\"\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "if \"highlight%28r=-1%2F2%29\":\r
\n" ); document.write( "\n" ); document.write( "\"a%5B1%5D%2A%28-1%2F2%29%2Ba%5B1%5D%2A%28-1%2F2%29%5E2=36\"....eq.2\r
\n" ); document.write( "\n" ); document.write( "\"a%5B1%5D%2A%28-1%2F2%29%2Ba%5B1%5D%2A%281%2F4%29=36\"......multiply by \"4\"\r
\n" ); document.write( "\n" ); document.write( "\"-2a%5B1%5D%2Ba%5B1%5D=144\"
\n" ); document.write( "\"-a%5B1%5D=144\"
\n" ); document.write( "\"highlight%28a%5B1%5D=+-144%29\"\r
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\n" ); document.write( "\n" ); document.write( "so, there are two solutions:
\n" ); document.write( "1. \"highlight%28a%5B1%5D=+3%29\" and \"highlight%28r=3%29\"
\n" ); document.write( "2.\"highlight%28a%5B1%5D=+-144%29\" and \"highlight%28r=-1%2F2%29\"\r
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\n" ); document.write( "\n" ); document.write( "then the second term is:\r
\n" ); document.write( "\n" ); document.write( "if \"a%5B1%5D=+3\" and \"r=3\":\r
\n" ); document.write( "\n" ); document.write( "\"a%5B2%5D=3%2A3\"
\n" ); document.write( "\"a%5B2%5D=9\"\r
\n" ); document.write( "\n" ); document.write( "third term is\r
\n" ); document.write( "\n" ); document.write( "\"a%5B3%5D=3%2A3%5E2\"
\n" ); document.write( "\"a%5B3%5D=27\"\r
\n" ); document.write( "\n" ); document.write( "fourth term
\n" ); document.write( "\"a%5B4%5D=3%2A3%5E3\"
\n" ); document.write( "\"a%5B4%5D=3%2A27\"
\n" ); document.write( "\"a%5B4%5D=81\"\r
\n" ); document.write( "\n" ); document.write( "the terms of sequence are:=>\"3%2C9%2C27%2C81\"\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "if \"a=-144\",\"r=-1%2F2\"\r
\n" ); document.write( "\n" ); document.write( "\"a%5B2%5D=+-144%2A%28-1%2F2%29%5E1\"\r
\n" ); document.write( "\n" ); document.write( "\"a%5B2%5D=-144%2F-2\"\r
\n" ); document.write( "\n" ); document.write( "\"a%5B2%5D=72\".\r
\n" ); document.write( "\n" ); document.write( "third term is\r
\n" ); document.write( "\n" ); document.write( "\"a%5B3%5D=-144%2A%28-1%2F2%29%5E2\"\r
\n" ); document.write( "\n" ); document.write( "\"a%5B3%5D=+-144%281%2F4%29\"\r
\n" ); document.write( "\n" ); document.write( "\"a%5B3%5D=+-36\"\r
\n" ); document.write( "\n" ); document.write( "and fourth term is\r
\n" ); document.write( "\n" ); document.write( "\"a%5B4%5D=+-144%2A%28-1%2F2%29%5E3\" \r
\n" ); document.write( "\n" ); document.write( "\"a%5B4%5D=+-144%28-1%2F8%29\"\r
\n" ); document.write( "\n" ); document.write( "\"a%5B4%5D=18\"\r
\n" ); document.write( "\n" ); document.write( "the terms of sequence are:=>\"-144%2C72%2C-36%2C18\"\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "now, check given data:\r
\n" ); document.write( "\n" ); document.write( "for =>\"3%2C9%2C27%2C81\"\r
\n" ); document.write( "\n" ); document.write( "\"a%5B4%5D=a%5B3%5D+%2B54\"....eq.1
\n" ); document.write( "\"81=27+%2B54\"
\n" ); document.write( "\"81=81\"\r
\n" ); document.write( "\n" ); document.write( "\"a%5B2%5D%2Ba%5B3%5D=36\"....eq.2
\n" ); document.write( "\"9%2B27=36\"
\n" ); document.write( "\"36=36\"\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "for =>\"-144%2C72%2C-36%2C18\"\r
\n" ); document.write( "\n" ); document.write( "\"a%5B4%5D=a%5B3%5D+%2B54\"....eq.1
\n" ); document.write( "\"18=-36+%2B54\"
\n" ); document.write( "\"18=18\"\r
\n" ); document.write( "\n" ); document.write( "\"a%5B2%5D%2Ba%5B3%5D=36\"....eq.2
\n" ); document.write( "\"72%2B%28-36%29=36\"
\n" ); document.write( "\"36=36\"\r
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