## Geometry: Common Core (15th Edition)

$\angle ECD=155$
$\angle ECD$ and $\angle BCD$ are a linear pair. From exercise 34, we know $m\angle BCD$ is 25 degrees. Use the definition of a linear pair: $\angle ECD+\angle BCD=180$ $\angle ECD+25=180$ $\angle ECD+25-25=180-25$ $\angle ECD=155$