document.write( "Question 1092202: The sum of the first two terms of a geometric series is 90. The third term is 24.\r
\n" ); document.write( "\n" ); document.write( "A. Show That there are two possible series and find the term and the common ration in each case.\r
\n" ); document.write( "\n" ); document.write( "B. Show that both series converge and find their respective sums.
\n" ); document.write( "

Algebra.Com's Answer #706781 by greenestamps(13330)\"\" \"About 
You can put this solution on YOUR website!


\n" ); document.write( "The third term is 24:

\n" ); document.write( "\"ar%5E2=24\"
\n" ); document.write( "--> \"a+=+24%2Fr%5E2\" (1)

\n" ); document.write( "The sum of the first two terms is 90:

\n" ); document.write( "\"a%2Bar+=+a%281%2Br%29+=+90\" (2)

\n" ); document.write( "Substitute (1) into (2):

\n" ); document.write( "\"%2824%2Fr%5E2%29%281%2Br%29+=+90\"
\n" ); document.write( "\"24%281%2Br%29+=+90r%5E2\"
\n" ); document.write( "\"90r%5E2-24r-24+=+0\"
\n" ); document.write( "\"15r%5E2-4r-4+=+0\"
\n" ); document.write( "\"%285r%2B2%29%283r-2%29+=+0\"

\n" ); document.write( "The two values of the common ratio are -2/5 and 2/3.

\n" ); document.write( "For the common ratio -2/5, the first term a is

\n" ); document.write( "\"24%2F%28-2%2F5%29%5E2+=+24%2F%284%2F25%29+=+150\"

\n" ); document.write( "That gives us the sequence 150, -60, 24, ...

\n" ); document.write( "For the common ratio 2/3, the first term a is

\n" ); document.write( "\"24%2F%282%2F3%29%5E2+=+24%2F%284%2F9%29+=+54\"

\n" ); document.write( "That gives us the sequence 54, 36, 24, ...
\n" ); document.write( "
\n" );