Find the value of `x^3+7x^2-x+1,\ w h e n\ x=1+2idot`

Explanation

To find the value of the expression \( x^3 + 7x^2 - x + 1 \) when \( x = 1 + 2i \), we will substitute \( x \) into the expression and simplify step by step.

### Step 1: Substitute \( x \)
We start by substituting \( x = 1 + 2i \) into the expression:

\[ x^3 + 7x^2 - x + 1 = (1 + 2i)^3 + 7(1 + 2i)^2 - (1 + 2i) + 1 \]
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