Que: Which of the following series is called the “formal power series”?

a. b₀+b₁x+b₂x²+…+bₙxⁿ

b. b₁x+b₂x²+…+bₙxⁿ

c. 1/2b₀+1/3b₁x+1/4b₂x²+…+1/nbₙxⁿ