Question

determine o 12° termo da P.A (1,-7, -15 -23) ​

Answer 1

P.A = (1,-7, -15 -23, ...)

Razão (r) = -8

an = a1 + r . (n-1)

an = 1 + (-8) . (n-1)

an = 1 + (-8n) + 8

an = 1 - 8n + 8

an = 9 - 8n

an = 9 - 8n

a12 = 9 - 8 . 12

a12 = 9 - 96

a12 = -87

Letra C.