Question

Exercícios P.A. Agradeço a força.

Answer 1

1) Sn=n(a1+an)
---------
2
an=a1+(n-1).R
A8=3+(8-1).5
A8=3+9.5
A8=3+45
A8=48

Sn=n(a1+an)/2
S8=8(3+48)/2
S8=8(51)/2
S8=408/2
S8=204


2)A3=a1+2r
0=a1+2.-2
0=a1-4
0+4=a1
4=a1

An=a1+(n-1).R
A12=4+(12-1).-2
A12=4+(11).-2
A12=4+(-22)
A12=4-22
A12=-18

Sn=n(a1+an)/2
S12=12(4+(-18))/2
S12=12(4-18)/2
S12=12(-14)/2
S12=-168/2
S12=-84

3)a7=5
a15=61

a15=a7+8r
61=5+8r
61-5=8r
56=8r
56/8=r
7=r

4)an=2n-1
A3=?
A3=2.3-1
A3=6-1
A3=5


SÓ CONSEGUI ESSAS, SORRY