1. The problem asks if for part 3, the equation should be $b - a = c - d$ given that $a$ and $c$ are opposite points. 2. To analyze this, let's recall what it means for points to be opposite in a geometric or algebraic context. Opposite points often imply a certain symmetry or equality in distances or coordinates. 3. If $a$ and $c$ are opposite points, then the vector or difference between $b$ and $a$ should equal the vector or difference between $c$ and $d$ for the equation $b - a = c - d$ to hold. 4. This means the displacement from $a$ to $b$ is the same as from $d$ to $c$, which aligns with the idea of opposite points creating equal and opposite segments. 5. Therefore, yes, if $a$ and $c$ are opposite points, the equation $b - a = c - d$ is correct and consistent with the properties of opposite points. Final answer: $b - a = c - d$ is correct under the condition that $a$ and $c$ are opposite points.