Respostas

2014-06-11T10:46:29-03:00
a_{8} =52

a_{10} =66

a_{n} =a_{1} +(n-1).r

a_{8} =a_{1} +7r52=a_{1} +7ra_{1} =52-7r

a_{10} =a_{1} +9r66 =a_{1} +9r=52-7r+9r=52+2r2r=66-52=14r=7

a_{1} =52-7r=52-7.7=52-49=3

a_{9} =3 +8.7=3+56=59
1 5 1
2014-06-11T10:56:02-03:00
A8= 52
A9= 59
A10= 66
então,
A10-A9=r
r=66-59
r=7

ok?