Question

The 10th term of an arithmetic sequence is 28 and the 7th term is -20 determine the first 4 terms​

Answer 1

Resposta:

PA(-116, -100, -84, -68)

Explicação passo a passo:

$a_1_0=a_7+3r\\28=-20+3r\\3r=48\\r =16\\ a_1+6r=a_7\\a_1+6.16=-20\\a_1=-20-96\\a_1=-116\\PA(-116, -100,-84,-68)$

Answer 2

Vamos là.

a10 = a1 + 9r = 28

a7 = a1 + 6r = -20

9r - 6r = 28 + 20 = 48

3r = 48

razão

r = 16

valor de a1

a1 + 9r = 28

a1 + 9*16 = 28

a1 = 28  - 144

a1 = -116

os 4 primeiros termos

a1 = -116

a2 = -116 + 16 = -100

a3 = -100 + 16 = -84

a4 = -84 + 16 = -68