document.write( "Question 1128311: 2) The third term of a G.P 12 and the first term is 48. Find the sum of the first 11 terms. \n" ); document.write( "
Algebra.Com's Answer #744802 by KMST(5328)\"\" \"About 
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WE are given:
\n" ); document.write( "\"b%5B1%5D=48\"= the first term
\n" ); document.write( "\"b%5B3%5D=12\"= the third term
\n" ); document.write( "
\n" ); document.write( "For a G.P. (geometric progression, geometric sequence in the USA),
\n" ); document.write( "with a common ratio \"r\" , the \"n%5Eth\" term is
\n" ); document.write( "\"b%5Bn%5D=b%5B1%5D%2Ar%5E%28n-1%29\"
\n" ); document.write( "The third term is given by that \"formula\" for \"n=3\" as
\n" ); document.write( "\"b%5B3%5D=b%5B1%5D%2Ar%5E%283-1%29=b%5B1%5D%2Ar%5E2\"
\n" ); document.write( "Substituting into \"b%5B3%5D=b%5B1%5D%2Ar%5E2\"
\n" ); document.write( "\"48\" for \"b%5B1%5D\" and \"12\" for \"b%5B3%5D\" we get
\n" ); document.write( "\"12=48%2Ar%5E2\"
\n" ); document.write( "\"12%2F48=r%5E2\"
\n" ); document.write( "\"1%2F4=r%5E2\"
\n" ); document.write( "Without more information, we cannot tell
\n" ); document.write( "if \"r=1%2F2=0.5\" or \"r=-1%2F2=-0.5\"
\n" ); document.write( "
\n" ); document.write( "For a G.P. the sum of the first \"n\" terms is given by
\n" ); document.write( "\"S%5Bn%5D=b%5B1%5D%28r%5En-1%29%2F%28r-1%29\"
\n" ); document.write( "
\n" ); document.write( "For \"n=11\" we get
\n" ); document.write( "\"S%5B11%5D=48%28r%5E11-1%29%2F%28r-1%29\"
\n" ); document.write( "
\n" ); document.write( "IF \"r=0.5\" :
\n" ); document.write( "\"S%5B11%5D=48%280.5%5E11-1%29%2F%280.5-1%29\"
\n" ); document.write( "\"S%5B11%5D=48%280.000244140625-1%29%2F%28-0.5%29\"
\n" ); document.write( "\"S%5B11%5D=48%28-0.999755859375%29%2F%28-0.5%29\"
\n" ); document.write( "\"S%5B11%5D=48%2A0.4998779296875\"
\n" ); document.write( "\"S%5B11%5D=95.953125\"
\n" ); document.write( "
\n" ); document.write( "IF \"r=-0.5\" :
\n" ); document.write( "\"S%5B11%5D=48%28%28-0.5%29%5E11-1%29%2F%28-0.5-1%29\"
\n" ); document.write( "......
\n" ); document.write( "\"S%5B11%5D=48%280.000244140625-1%29%2F%28-1.5%29\"
\n" ); document.write( "...............
\n" ); document.write( "\"S%5B11%5D=32.015625\"
\n" ); document.write( "
\n" );