The relationship between ∠COB and ∠BOA is that they are adjacent angles. Adjacent angles share a common vertex and a side, but do not overlap.
If you know that ∠COB and ∠BOA together make a straight angle (180 degrees), you can write the following equation to solve for the measure of ∠COB:
\[ \text{m} \angle COB + \text{m} \angle BOA = 180^\circ \]
If you have the measure of ∠BOA, you can substitute it into the equation to find ∠COB:
\[ \text{m} \angle COB = 180^\circ - \text{m} \angle BOA \]
This equation can be used to find the measure of ∠COB.