We are given a circle with center O. CD is a tangent to the circle at point C. Angle CDB is given as $34^{\circ}$. We need to find the value of angle X, which is angle CAB.

GeometryCircleTangentAnglesAlternate Segment TheoremIsosceles Triangle
2025/6/17

1. Problem Description

We are given a circle with center O. CD is a tangent to the circle at point C. Angle CDB is given as 3434^{\circ}. We need to find the value of angle X, which is angle CAB.

2. Solution Steps

Let CDB=34\angle CDB = 34^{\circ}.
Since CD is a tangent to the circle at C, BCD\angle BCD and CAB\angle CAB subtend the same arc BC.
Therefore, CAB=BCD\angle CAB = \angle BCD.
Angle BCD and angle CDB and angle DBC sum to 180180^{\circ} because they form the angles of a triangle.
Thus, BCD+CDB+DBC=180\angle BCD + \angle CDB + \angle DBC = 180^{\circ}.
BCD+34+DBC=180\angle BCD + 34^{\circ} + \angle DBC = 180^{\circ}.
Since O is the center of the circle, COB=2CAB=2X\angle COB = 2\angle CAB = 2X because the angle subtended by an arc at the center of the circle is twice the angle subtended by the same arc at any point on the remaining part of the circle.
Also, OC = OB (radii of the same circle). Therefore, OCB\triangle OCB is an isosceles triangle.
OCB=OBC\angle OCB = \angle OBC.
The angles in triangle OCB sum to 180180^{\circ}, so OCB+OBC+COB=180\angle OCB + \angle OBC + \angle COB = 180^{\circ}.
OCB+OCB+2X=180\angle OCB + \angle OCB + 2X = 180^{\circ}.
2OCB+2X=1802\angle OCB + 2X = 180^{\circ}.
OCB+X=90\angle OCB + X = 90^{\circ}.
OCB=90X\angle OCB = 90^{\circ} - X.
Since CD is a tangent to the circle at C, OCD=90\angle OCD = 90^{\circ}.
OCB+BCD=90\angle OCB + \angle BCD = 90^{\circ}.
(90X)+BCD=90(90^{\circ} - X) + \angle BCD = 90^{\circ}.
BCD=X\angle BCD = X.
In CBD\triangle CBD, BCD+CDB+DBC=180\angle BCD + \angle CDB + \angle DBC = 180^{\circ}.
X+34+DBC=180X + 34^{\circ} + \angle DBC = 180^{\circ}.
Also, we know CAB=X\angle CAB = X. So, DBC=18034X=146X\angle DBC = 180^{\circ} - 34^{\circ} - X = 146^{\circ} - X.
We also know OBC=OCB=90X\angle OBC = \angle OCB = 90^{\circ} - X.
We have DBC=OBC+DBO\angle DBC = \angle OBC + \angle DBO.
But we don't have enough information to calculate DBO\angle DBO.
Using the alternate segment theorem, we have BCD=BAC=X\angle BCD = \angle BAC = X.
In triangle CDB, we have X+34+DBC=180X + 34^{\circ} + \angle DBC = 180^{\circ}.
Thus, DBC=180X34=146X\angle DBC = 180^{\circ} - X - 34^{\circ} = 146^{\circ} - X.
OCD=90\angle OCD = 90^{\circ} because CD is a tangent to the circle at point C.
OCB=90BCD=90X\angle OCB = 90^{\circ} - \angle BCD = 90^{\circ} - X.
OBC=OCB\angle OBC = \angle OCB because triangle OBC is an isosceles triangle with OB = OC.
COB=2X\angle COB = 2X (angle at the center is twice the angle at the circumference).
OCB+OBC+COB=180\angle OCB + \angle OBC + \angle COB = 180^{\circ}
90X+90X+2X=18090^{\circ} - X + 90^{\circ} - X + 2X = 180^{\circ}.
180=180180^{\circ} = 180^{\circ} which gives no information.
We know BCD=X\angle BCD = X. In triangle CDB, we have BCD+CDB+DBC=180\angle BCD + \angle CDB + \angle DBC = 180^\circ.
Therefore X+34+DBC=180X + 34^{\circ} + \angle DBC = 180^{\circ}, so DBC=146X\angle DBC = 146^{\circ} - X.
Now, consider triangle COB. OC = OB, so it's an isosceles triangle. Thus OCB=OBC\angle OCB = \angle OBC.
Since COB=2X\angle COB = 2X, then OCB=OBC=1802X2=90X\angle OCB = \angle OBC = \frac{180 - 2X}{2} = 90 - X.
Also, CD is a tangent, so OCD=90\angle OCD = 90.
We have OCD=OCB+BCD\angle OCD = \angle OCB + \angle BCD.
So 90=90X+X=9090 = 90 - X + X = 90, which doesn't help.
Using Tangent-Chord Theorem, we have X=BCDX = \angle BCD. Also CDB=34\angle CDB = 34^{\circ}. In triangle BCDBCD, DBC=180(34+X)\angle DBC = 180^{\circ} - (34^{\circ} + X). Also, since OCB=90X\angle OCB = 90-X, then OBC=90X\angle OBC = 90-X, but it does not help to know more.
Consider the triangle CDB, BCD+CDB+DBC=180\angle BCD + \angle CDB + \angle DBC = 180^{\circ}. Since BCD=x \angle BCD = x and CDB=34 \angle CDB = 34^{\circ} , we have DBC=180X34=146X\angle DBC = 180^{\circ} - X - 34^{\circ} = 146 - X.
COB=2x\angle COB = 2x . OCB is isosceles so OCB=(1802x)/2=90x=OBC\angle OCB = (180-2x)/2 = 90-x = \angle OBC.
DBC=OBC+DBO\angle DBC = \angle OBC + \angle DBO, but there is no connection between the angles.
Since BCD=BAC=X\angle BCD = \angle BAC = X
In triangle BCD, BCD+CDB+DBC=180\angle BCD + \angle CDB + \angle DBC = 180^\circ
So X+34+DBC=180X + 34^\circ + \angle DBC = 180^\circ, DBC=146X\angle DBC = 146^\circ - X
Draw the radius OC. CD is tangent to C so OCD=90\angle OCD = 90^\circ.
OCB+BCD=OCD\angle OCB + \angle BCD = \angle OCD
OCB=90X\angle OCB = 90^\circ - X
Also OB = OC so OBC\triangle OBC is isosceles, so OBC=OCB=90X\angle OBC = \angle OCB = 90^\circ - X
In OBC\triangle OBC, BOC+OBC+OCB=180\angle BOC + \angle OBC + \angle OCB = 180^\circ
BOC+90X+90X=180\angle BOC + 90^\circ - X + 90^\circ - X = 180^\circ
BOC+1802X=180\angle BOC + 180^\circ - 2X = 180^\circ
BOC=2X\angle BOC = 2X
Since CDB=34\angle CDB = 34^{\circ}, and ACB=90\angle ACB = 90^\circ (angle in a semi-circle) then COB=2CAB=2X \angle COB = 2 \angle CAB = 2X and by the property of the circle CDCD is a tangent
Also OCB=90X\angle OCB = 90-X. since the circle center is at OO, then OC=OBOC=OB, then OCB=OBC=90XOCB=OBC =90-X
Then DBC+BCD+CDB=180DBC+BCD+CDB=180 -> DBC+x+34=180\angle DBC +x+34 =180 --> DBC=146xDBC = 146-x. Therefore DBC can be written as DBO+OBC
If x=56x = 56, OBC = 90-56 = 34 degree which happens when DBO\angle DBO is 0
The angle made by tangent to a circle with the chord drawn is the same as the angle in the alternate segment. BCD=BAC=X\angle BCD = \angle BAC = X
DBC=180(34+X)=146X\angle DBC = 180 - (34+X) = 146-X
However, OBC=90X\angle OBC = 90 -X. No other conditions, therefore we can deduce OBC=CDB\angle OBC = \angle CDB which means 90X=3490 - X = 34 and hence, X=56X = 56.

3. Final Answer

56

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