We are given a cyclic quadrilateral $ABCD$ inscribed in a circle. We know that $\angle DBC = 47^\circ$ and $\angle ADB = 28^\circ$. We want to find the measure of the angle $\angle DCP$.

GeometryCyclic QuadrilateralAngles in a CircleAngle ChasingGeometric Proof
2025/4/9

1. Problem Description

We are given a cyclic quadrilateral ABCDABCD inscribed in a circle. We know that DBC=47\angle DBC = 47^\circ and ADB=28\angle ADB = 28^\circ. We want to find the measure of the angle DCP\angle DCP.

2. Solution Steps

Since ABCDABCD is a cyclic quadrilateral, the vertices AA, BB, CC, and DD lie on the circumference of the circle.
Since angles subtended by the same chord are equal, we have DAC=DBC=47\angle DAC = \angle DBC = 47^\circ.
Also, ACB=ADB=28\angle ACB = \angle ADB = 28^\circ.
We know that the sum of angles in ADC\triangle ADC is 180180^\circ. Therefore, ACD=180DACADC=1804728=105\angle ACD = 180^\circ - \angle DAC - \angle ADC = 180^\circ - 47^\circ - 28^\circ = 105^\circ.
Since ABCDABCD is a cyclic quadrilateral, we have ABC+ADC=180\angle ABC + \angle ADC = 180^\circ, and BAD+BCD=180\angle BAD + \angle BCD = 180^\circ.
We have BCD=BCA+ACD=28+105=133\angle BCD = \angle BCA + \angle ACD = 28^\circ + 105^\circ = 133^\circ.
Since CDPCDP is a straight line, DCP+BCD=180\angle DCP + \angle BCD = 180^\circ.
DCP=180BCD\angle DCP = 180^\circ - \angle BCD.
We can also write DCP=DAB\angle DCP = \angle DAB.
DAB=DAC+CAB\angle DAB = \angle DAC + \angle CAB.
Also, CAB=CDB\angle CAB = \angle CDB.
We are given DBC=47\angle DBC = 47^\circ and ADB=28\angle ADB = 28^\circ.
Since CAB=CDB\angle CAB = \angle CDB, and quadrilateral ABCDABCD is cyclic, we have CDB=CAB\angle CDB = \angle CAB. Also CAB=CDB=28\angle CAB = \angle CDB = 28^\circ.
So DAB=DAC+CAB=47+28=75\angle DAB = \angle DAC + \angle CAB = 47^\circ + 28^\circ = 75^\circ.
Since DCP=180BCD\angle DCP = 180^\circ - \angle BCD, and BCD+DAB=180\angle BCD + \angle DAB = 180^\circ, then DCP=DAB=75\angle DCP = \angle DAB = 75^\circ.

3. Final Answer

75 degrees

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