If `x^3+3x^2-9x+c` is of the form `(x-alpha)^2(x-beta)` then `c` is equal to

Explanation

To solve the problem, we need to find the value of \( c \) such that the polynomial \( f(x) = x^3 + 3x^2 - 9x + c \) can be expressed in the form \( (x - \alpha)^2 (x - \beta) \).

### Step-by-Step Solution:

1. **Identify the form of the polynomial**:
Given \( f(x) = x^3 + 3x^2 - 9x + c \), we need to differentiate it to find \( f'(x) \).

2. **Differentiate the polynomial**:
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