Question

Determine a soma dos 7 primeiros termos da PG (42,126,..)

Answer 1

A₁ = 42
Q = 3
A₇ = ?

A₇ = A₁ * Q ⁿ⁻¹
A₇ = 42 * 3 ⁶⁻¹
A₇ = 42 * 3 ⁵
A₇ = 42 * 243
A₇ = 10206

S n = A₁ ( Q ⁿ - 1 ) / Q - 1
S n = 42 ( 3 ⁷⁻¹ ) / 3 - 1
S n = 42 * 729 / 2
S n = 30618 / 2
S n = 15309