The property used to arrive at Line 1, where the student rewrote the equation from \( x + 2(x + 1) = 17 \) to \( x + 2x + 2 = 17 \), is the Distributive Property. This property allows you to distribute a multiplication over addition or subtraction. Here, \( 2 \) was distributed to both \( x \) and \( 1 \) in the expression \( 2(x + 1) \).
So the correct response is:
Distributive Property