Question

Escreva uma P.A de seis termos em que:

a) a1=-4 e r=6
b) a1=-2 e r=-4
c) a2=1 e a3=-7
d) a2=9 e r=1

Answer 1

a) a 1 = -4 e r = 6
a 2 = a 1 + r = -4 + 6 = 2
a 3 = a 2 + r = 2 + 6 = 8
a 4 = a 3 + r = 8 + 6 = 14
a 5 = a 4 + r = 14 + 6 = 20
a 6 = a 5 + r = 20 + 6 = 26
P.A.(-4;2;8;14;20;26 )

b)a 1 = -2 e r = - 4
a 2 = a 1 + r = -2 - 4 = - 6
a 3 = a 2 + r = -6 - 4 = -10
a 4 = a 3 + r = -10  - 4 = -14
a 5 = a 4 + r = -14 - 4 = - 18
a 6 = a 5 + r = -18 - 4 =  - 22
P.A.(-2;-6;-10;-14;-18;-22)

c)a 2 = 1  e a 3 = - 7
r = a 3 - a 2
r = -7 - 1 = -8
r = -8
r = a 2 - a 1
a 2 - a 1 = r
a 2 = r + a 1
a 2 - r = a 1
1 + 8 = a 1
a 1 = 9
a 2 = 1
a 3 =  -7
a 4 = a 3 + r = -7 - 8 = -15
a 5 = a 4 + r = -15 - 8 = -23
a 6 = a 5 + r = -23 - 8 = - 31
P.A.(9;1;-7;-15;-23;-31 )
    a 1  = 8
d)a 2 = 9 e r = 1
a 3 = a 2 + r = 9 + 1 = 10
a 4 = a 3 + r = 10 + 1 = 11
a 5 = a 4 + r = 11 + 1 = 12
a 6 = a 5 + r = 12 + 1 = 13
P.A.(8,9,10,11,12,13 )

r = a 2 - a 1
a 2 - a 1 = r
a 2 = r + a 1
a 2 - r = a 1
9 - 1 = a 1
a 1 = 8