To identify the step that contains an error using the Commutative Property of Addition, let's analyze each step in detail:
Step 1: \[ 8 + 4 + x^2 - x^2 + 17x = 10 + 2 + 10x - 4x^2 + 7x + 4x^2 \]
- This step correctly organizes the terms.
Step 2: \[ 8 + 4 + 17x + x^2 - x^2 = 10 + 2 + 4x^2 - 4x^2 + 10x + 7x \]
- In the left-hand side, \( x^2 - x^2 \) correctly cancels out. However, we need to verify the right-hand side:
- On the right side, \( 10 + 2 + (10x + 7x) + (4x^2 - 4x^2) \) should combine as follows: \( 10 + 2 + 10x + 7x \) which simplifies to \( 12 + 17x \), and the \( 4x^2 - 4x^2 \) cancels to 0.
- Therefore, the right-hand side is indeed \( 12 + 17x \), just like the left side.
Step 3: \[ 12 + 17x + x^2 = 12 - x^2 + 17x \]
- This is where we find the error. The left side has \( x^2 \) and the right side has \( -x^2 \). These terms are not equivalent.
From the analysis, the error occurs in Step 3 since it presents a false equivalence of \( x^2 \) and \( -x^2 \) which is not valid.
Therefore, the answer is Step 3.