#### Problem Statement: ECE Board November 1995

What is the sum of the coefficients of the expansion (2x–1)^20?

- A. 0
- B. 1
- C. 2
- D. 3

#### Problem Answer:

The sum of the coefficients of the expansion is **0**.

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Why did you subract negative 1 from (2x-1)^20?

Why subtract to -1. I though the answer is 1 ? (2-1)^20

I solve it manually, the sum is 1

Sum is 1

if 2nd term is constant then:

Sum of coef. = (coef. of X + k)^n – (k)^n

thus, S = [2+(-1)]^20 – (-1)^20

= 0