document.write( "Question 888275: Find the sum of all 15 terms in a sequence 7, 3, -1, -5 ...tn, \n" ); document.write( "
Algebra.Com's Answer #537269 by richwmiller(17219)\"\" \"About 
You can put this solution on YOUR website!
S = ½(a + an)n
\n" ); document.write( "S = ½(2a + (n-1)d)n
\n" ); document.write( "an = a + (n - 1)d
\n" ); document.write( "
\n" ); document.write( "We will use
\n" ); document.write( "S = ½(2a + (n-1)d)n
\n" ); document.write( "since we don't know the 15th term
\n" ); document.write( "S = ½(2*7 + (14)(-4))15
\n" ); document.write( "S = (7 + (7)(-4))15
\n" ); document.write( "S = (7 -28)15
\n" ); document.write( "S = (-21)15
\n" ); document.write( "S=-315\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( " \n" ); document.write( "
\n" );