Final answer:
The missing justification in the proof is the distributive property of equality, which allows multiplication across a sum or difference in an equation, including in vector operations like the cross product. The correct answer is option O distributive property of equality
Step-by-step explanation:
The missing justification in the proof based on the provided information is the distributive property of equality. This property indicates that if you have a term being multiplied by a sum or difference, you can distribute the multiplication over the addition or subtraction. For example, in vector operations, specifically with the cross product, the distributive property is given by A × (B + C) = A × B + A × C.
This is used frequently when working with vector components in Cartesian coordinates. When working with equations, this property allows us to maintain equality by ensuring that when we multiply or divide both sides of an equation by the same number, we apply it to each term within brackets.