## Thomas' Calculus 13th Edition

Both two vectors $\overrightarrow{CA}$ and $\overrightarrow{CB}$ are orthogonal.
Let $\overrightarrow{CA}$ and $\overrightarrow{CB}$ be the two vectors. Now, $(-v+(-u)) \cdot (-v+u)=v \cdot v-v \cdot u+u \cdot v -u \cdot u$ and $v \cdot v-v \cdot u+u \cdot v -u \cdot u=|v|^2-|u|^2$ when the both vectors posses same radius of circle then we have $|v|^2 =|u|^2$ This implies that $|v|^2-|u|^2=|v|^2-|v|^2=0$ Hence, we conclude that both two vectors $\overrightarrow{CA}$ and $\overrightarrow{CB}$ are orthogonal.