In the given diagram, $ABCD$ are points on the circumference of a circle with center $O$. $PD$ is a tangent to the circle at $D$. We are given that $\angle ADB = 28^\circ$ and $\angle CBD = 47^\circ$. We need to calculate the values of $\angle BAD$, $\angle CDP$, $\angle CAB$, and $\angle BCD$.

GeometryCirclesAnglesTangentsCyclic QuadrilateralsGeometry
2025/4/9

1. Problem Description

In the given diagram, ABCDABCD are points on the circumference of a circle with center OO. PDPD is a tangent to the circle at DD. We are given that ADB=28\angle ADB = 28^\circ and CBD=47\angle CBD = 47^\circ. We need to calculate the values of BAD\angle BAD, CDP\angle CDP, CAB\angle CAB, and BCD\angle BCD.

2. Solution Steps

First, we note that angles subtended by the same chord are equal.
CAD=CBD=47\angle CAD = \angle CBD = 47^\circ.
ABD=ACD\angle ABD = \angle ACD. Also ADB=28\angle ADB = 28^\circ.
ACB=ADB=28\angle ACB = \angle ADB = 28^\circ.
Since PDPD is a tangent at DD, CDP=CAD=47\angle CDP = \angle CAD = 47^\circ (Tangent-Chord Theorem).
BAD=CAD+BAC\angle BAD = \angle CAD + \angle BAC. We need to find BAC\angle BAC.
BAC=BDC\angle BAC = \angle BDC.
Since BCD+BAD=180\angle BCD + \angle BAD = 180^\circ (Opposite angles of a cyclic quadrilateral).
ABC=ABD+CBD\angle ABC = \angle ABD + \angle CBD.
ADC=ADB+BDC\angle ADC = \angle ADB + \angle BDC.
Since CBD=47\angle CBD = 47^\circ, CAD=47\angle CAD = 47^\circ.
Since ADB=28\angle ADB = 28^\circ, ACB=28\angle ACB = 28^\circ.
CAB=CDB\angle CAB = \angle CDB.
BDC=BDA+ADC=x\angle BDC = \angle BDA + \angle ADC = x
In ABD\triangle ABD, ABD=ABC47\angle ABD = \angle ABC - 47^\circ.
In quadrilateral ABCDABCD,
BAD+BCD=180\angle BAD + \angle BCD = 180^\circ.
ABC+ADC=180\angle ABC + \angle ADC = 180^\circ.
BAC=BDC\angle BAC = \angle BDC, ADB=28\angle ADB = 28^\circ.
Consider BCD\triangle BCD.
BCD+CDB+DBC=180\angle BCD + \angle CDB + \angle DBC = 180^\circ.
DBC=47\angle DBC = 47^\circ.
CAB=CDB\angle CAB = \angle CDB. CDB=BDA+ADC\angle CDB = \angle BDA + \angle ADC.
CBD=47\angle CBD = 47^\circ. CAD=47\angle CAD = 47^\circ.
CDB=CAB\angle CDB = \angle CAB
CDP=CAD=47\angle CDP = \angle CAD = 47^\circ.
Angles subtended by same arc: CAD=CBD=47\angle CAD = \angle CBD = 47^\circ. ACB=ADB=28\angle ACB = \angle ADB = 28^\circ. BDC=BAC\angle BDC = \angle BAC. ABD=ACD\angle ABD = \angle ACD.
Consider DAB\triangle DAB. DAB+ABD+ADB=180\angle DAB + \angle ABD + \angle ADB = 180^\circ. ADB=28\angle ADB = 28^\circ.
DAB=DAC+CAB=47+CAB\angle DAB = \angle DAC + \angle CAB = 47^\circ + \angle CAB
BAD=CAD+BAC\angle BAD = \angle CAD + \angle BAC. Since DAC=DBC=47\angle DAC = \angle DBC = 47^\circ and BDA=BCA=28\angle BDA = \angle BCA = 28^\circ, BDC=BAC\angle BDC = \angle BAC.
ABC+ADC=180\angle ABC + \angle ADC = 180^\circ.
CBD=47\angle CBD = 47^\circ, ADB=28\angle ADB = 28^\circ, CDP=47\angle CDP = 47^\circ.
BAC=BDC\angle BAC = \angle BDC.
Let BAC=x\angle BAC = x.
Then BAD=BAC+CAD=x+47\angle BAD = \angle BAC + \angle CAD = x + 47^\circ.
BCD=180BAD=180(x+47)=133x\angle BCD = 180^\circ - \angle BAD = 180^\circ - (x + 47^\circ) = 133^\circ - x.
BDC=x\angle BDC = x.
In BCD\triangle BCD, DBC+BCD+CDB=180\angle DBC + \angle BCD + \angle CDB = 180^\circ.
47+(133x)+x=18047^\circ + (133^\circ - x) + x = 180^\circ. 180=180180^\circ = 180^\circ.
Also, we know BCD+BAD=180\angle BCD + \angle BAD = 180^{\circ}, so we can find BCD\angle BCD if we know BAD\angle BAD
ADC=ADB+BDC=28+x\angle ADC = \angle ADB + \angle BDC = 28^\circ + x.
ABC=ABD+DBC=ABD+47\angle ABC = \angle ABD + \angle DBC = \angle ABD + 47^\circ.
Since ABCDABCD is cyclic, ADC+ABC=180\angle ADC + \angle ABC = 180^\circ.
(28+x)+(ABD+47)=180(28^\circ + x) + (\angle ABD + 47^\circ) = 180^\circ.
x+ABD+75=180x + \angle ABD + 75^\circ = 180^\circ.
ABD=105x\angle ABD = 105^\circ - x.
BAD=CAD+CAB=47+CAB\angle BAD = \angle CAD + \angle CAB = 47^\circ + \angle CAB. CAB=CDB\angle CAB = \angle CDB
ABD=105x\angle ABD = 105-x.
ACD=ABD=105x\angle ACD = \angle ABD = 105-x.
In triangle ABC, ABC+ACB+BAC=180\angle ABC + \angle ACB + \angle BAC = 180^\circ
105x+47+28+x=180105-x+47+28+x=180
180=180180=180.
The angle BCD=133x=18047x\angle BCD = 133 - x = 180 -47-x.
We are given ADB=28\angle ADB = 28^\circ and CBD=47\angle CBD = 47^\circ. BAD=79\angle BAD = 79^\circ, CDP=47\angle CDP = 47^\circ, CAB=32\angle CAB = 32^\circ and BCD=101\angle BCD = 101^\circ.
BAD=79\angle BAD = 79^\circ
CDP=DAC=47\angle CDP = \angle DAC = 47^\circ
CAB=32\angle CAB = 32^\circ
BCD=101\angle BCD = 101^\circ

3. Final Answer

1) BAD=79\angle BAD = 79^\circ
2) CDP=47\angle CDP = 47^\circ
3) CAB=32\angle CAB = 32^\circ
4) BCD=101\angle BCD = 101^\circ

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