Partial Sum

Question

S₅ of the sequence an = -8+(n-1)3

Answer 1

S₅ = (n/2)(2a₁ + (n - 1)d)

S₅ = (5/2)(2(-8) + 4(3))

S₅ = (5/2)(-16 + 12)

S₅ = (5/2)(-4)

S₅ = 5(-2)

S₅ = -10