document.write( "Question 212918: The question is: Three consecutive terms of a geometric sequence have a sum of 28 and a product of 512. Find these numbers.
\n" ); document.write( "(Hint: let these numbers be a/r, a and ar )\r
\n" ); document.write( "\n" ); document.write( "I really don't understand the question, anyone kindly help me??\r
\n" ); document.write( "\n" ); document.write( "Thanks
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Algebra.Com's Answer #160851 by josmiceli(19441)\"\" \"About 
You can put this solution on YOUR website!
A geometric sequence looks like:
\n" ); document.write( "7
\n" ); document.write( "7*3 = 21
\n" ); document.write( "21*3 = 63
\n" ); document.write( "63*3 = 189
\n" ); document.write( "108*3 = 567
\n" ); document.write( "The sequence is:
\n" ); document.write( "7,21,63,189,567
\n" ); document.write( "In the general formula, I call the nth term \"a%5Bn%5D\"
\n" ); document.write( "so,
\n" ); document.write( "\"a%5B1%5D+=+7\"
\n" ); document.write( "\"a%5B2%5D+=+21\"
\n" ); document.write( "etc.
\n" ); document.write( "The multiplier for each term, in this case, \"3\",
\n" ); document.write( "is called \"r\", and \"r+=+a%5Bn%2B1%5D%2Fa%5Bn%5D\"
\n" ); document.write( "All this is saying is:
\n" ); document.write( "\"324%2F108+=+3\"
\n" ); document.write( "\"108%2F36+=+3\"
\n" ); document.write( "\"36%2F21+=+3\"
\n" ); document.write( "\"21%2F7+=+3\"
\n" ); document.write( "Another general formula is:
\n" ); document.write( "\"a%5Bn%5D+=+a%5B1%5D%2Ar%5E%28n-1%29\"
\n" ); document.write( "Testing the formula:
\n" ); document.write( "\"a%5B1%5D+=+a%5B1%5D%2A3%5E0\"
\n" ); document.write( "\"a%5B2%5D+=+a%5B1%5D%2A3%5E1\"
\n" ); document.write( "\"a%5B3%5D+=+a%5B1%5D%2A3%5E2\"
\n" ); document.write( "\"a%5B4%5D+=+a%5B1%5D%2A3%5E3\"
\n" ); document.write( "\"a%5B5%5D+=+a%5B1%5D%2A3%5E4\"
\n" ); document.write( "If I plug in \"a%5B1%5D+=+7\", then I get
\n" ); document.write( "7,21,63,189,567
\n" ); document.write( "Now, refering back to your problem, they are just saying
\n" ); document.write( "\"a%5B1%5D+=+a\"
\n" ); document.write( "Then, using my formula again
\n" ); document.write( "\"a%5B1%5D+=+a%2Ar%5E0\"
\n" ); document.write( "\"a%5B2%5D+=+a%2Ar%5E1\"
\n" ); document.write( "\"a%5B3%5D+=+a%2Ar%5E2\"
\n" ); document.write( "\"a%5B4%5D+=+a%2Ar%5E3\"
\n" ); document.write( "\"a%5B5%5D+=+a%2Ar%5E4\"
\n" ); document.write( "The sequence is:
\n" ); document.write( "a, ar, ar^2, ar^3, ar^4
\n" ); document.write( "By suggesting that you use a/r, a, and ar, what
\n" ); document.write( "they are doing is starting the sequence with \"a%5B0%5D\"
\n" ); document.write( "instead of \"a%5B1%5D\", which still gives you a valid sequence
\n" ); document.write( "\"a%5B0%5D+=+a%2Ar%5E%28-1%29\"
\n" ); document.write( "\"a%5B1%5D+=+a%2Ar%5E0\"
\n" ); document.write( "\"a%5B2%5D+=+a%2Ar%5E1\"
\n" ); document.write( "\"a%5B3%5D+=+a%2Ar%5E2\"
\n" ); document.write( "The sequence is
\n" ); document.write( "a/r, a, ar, ar^2
\n" ); document.write( "Using my example with \"r+=+3\",
\n" ); document.write( "the terms would be:
\n" ); document.write( "7/3, 7, 21, 63, etc, which is still valid
\n" ); document.write( "Three consecutive terms of a geometric sequence have a sum of 28 and a product of 512, so
\n" ); document.write( "(1)\"a%2Fr+%2B+a+%2B+ar+=+28\"
\n" ); document.write( "(2)\"%28a%2Fr%29%2Aa%2Aar+=+512\"
\n" ); document.write( "\"a%5E3+=+512\"
\n" ); document.write( "\"a+=+8\"
\n" ); document.write( "Plugging this into the 1st equation,
\n" ); document.write( "(1)\"8%2Fr+%2B+8+%2B+8r+=+28\"
\n" ); document.write( "Multiply both sides by \"r\"
\n" ); document.write( "\"8+%2B+8r+%2B+8r%5E2+=+28\"
\n" ); document.write( "\"2+%2B+2r+%2B+2r%5E2+=+7\"
\n" ); document.write( "\"2r%5E2+%2B+2r+-+5+=+0\"
\n" ); document.write( "Use the quadratic formua:
\n" ); document.write( "\"r+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+\"
\n" ); document.write( "\"a+=+2\"
\n" ); document.write( "\"b+=+2\"
\n" ); document.write( "\"c+=+-5\"
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