Which of the following expresses 1+5+25+125+625+3125 in sigma notation?
6
(a) Σ (-5)ᵏ⁻¹
(k=1)
5
(b) Σ (-1)ᵏ(5)ᵏ
(k=0)
3
(c) Σ (-1)ᵏ⁺¹(5)ᵏ⁺²
(k=-2)