Solution:
15.
(i) \[PQ\]is a tangent and \[CD\]is a chord.
\[\angle DCQ\text{ }=\angle DBC\] [Angles in the alternate segment]
\[\angle DBC\text{ }=\text{ }{{40}^{o}}\]
\[[As\angle DCQ\text{ }=\text{ }{{40}^{o}}]\]
(ii) \[\angle DCQ\text{ }+\angle DCB\text{ }+\angle BCP\text{ }=\text{ }{{180}^{o}}\]
\[{{40}^{o}}~+\text{ }{{90}^{o}}~+\angle BCP\text{ }=\text{ }{{180}^{o}}~\]
\[[As\angle DCB\text{ }=\text{ }{{90}^{o}}]\]
\[\angle BCP\text{ }=\text{ }{{180}^{o}}-\text{ }{{130}^{o}}~\]
So,
\[=\text{ }{{50}^{o}}\]