Respostas

2013-08-29T23:56:44-03:00
Sn = [n(a1 + an)]/2
710 = [20(7 + a10)]/2
710 = 70 + 10a10
710 - 70 = 10a10
640 = 10a10
a10 = 640/10
a10 = 64