Mathematics

In a cyclic quadrilateral, opposite angles are supplementary—they always sum to $180°$. This is the key property that unlocks the problem: once you identify which angles are opposite, you can set up a single equation and solve for $x$. Since $A$ and $C$ are opposite vertices, their angle measures must add to $180°$.

In a cyclic quadrilateral, opposite angles are supplementary—they always sum to $180°$. This is the key property that unlocks the problem: once you identify which angles are opposite, you can set up a single equation and solve for $x$. Since $A$ and $C$ are opposite vertices, their angle measures must add to $180°$.