Question

Find a formula for a_n (for the geometric sequence), then find the 8th term. Solve for both or one of these questions, thank you so much!

Answer 1

2a. aₙ = 12 * -2ⁿ⁻¹; a₈ = -1536

2b. aₙ = 4 * 3ⁿ⁻¹; a₈ = 8748

Explanation:

The geometric sequence formula is aₙ = a₁ * rⁿ⁻¹.

2a:

a₈ = 12 * -2⁸⁻¹ {Subtract 1 from 8 to get 7}

a₈ = 12 * -2⁷ {2⁷ is 128. Since the exponent is odd, this will be negative.}

a₈ = 12 * (-128) {Multiply 12 by -128 to get -1536.

a₈ = -1536

2b:

a₈ = 4 * 3⁸⁻¹ {Subtract 1 from 8 to get 7)

a₈ = 4 * 3⁷ {7 is the 3rd number after 4 (a multiple of 4). As a result, this will end in a 7. 3⁷ is 2187.}

a₈ = 4 * 2187 {Multiply 4 by 2187 to get 8748}

a₈ = 8748