Find the sum of the first 12 terms of a geometric sequence where the first term is 256 and the common ratio is -1/2 . 170.625 341.3125 511.9375 511.875

Answer 1

S_n = a₁(1 - rⁿ) / (1 - r)

S₁₂ = 256( 1 - (-0.5)¹²) / (1 - (-0.5))

S₁₂ = 256(1 - 0.00024414) / (1.5)

S₁₂ = 256(0.99975586) / 1.5

S₁₂ = 155.9375 / 1.5

S₁₂ = 170.625