examday

/TMUA

Bonus question. In the coordinate plane, let $C$ be the reflection of the point $A(a,b)$ about the point $B(3,0)$, and let $D$ be the reflection of $A$ about the $y$-axis.

Given that the line through $C$ and $D$ has the equation $y=-x-1$, what is $a+b$?