1. Which reason completes the proof below?
Given: BC is tangent to Circle A at D
Prove: AB = AC

Answer:
(C)
Step-by-step explanation:
Given: BC is tangent to the circle A at D.
To prove: AB is congruent to AC
Proof:
Statements Reason
1. BC is tangent to the circle A at D. Given
2. DB≅DC Given
3.AD⊥BC If a line is tangent to a circle then it is perpendicular to the radius at the point of tangency.
4. ∠ADB and ∠ADC are right angles Definition of perpendicular lines
5. ∠ADB≅∠ADC Right angles are congruent
6. AD≅AD Reflexive property of congruence
7. ΔADB≅ΔADC SAS rule
8. AB≅AC CPCTC
Hence, option (C) is correct.
Tangent to a circle is straight line just touching the circle at one point. The reason to complete the proof is: If a line is tangent to a circle, then it is perpendicular to the point of tangency
A line segment which touches a circle specified to only one point is called a tangent to that circle.
There is a theorem in mathematics that:
If there is a circle O with tangent line L intersecting the circle at point A, then the radius OA is perpendicular to the line L.
For the given case, the missing statement for the proof is:
If a line is tangent to a circle, then it is perpendicular to the point of tangency(the point on circle where the tangent intersects it).
Hence, the reason to complete the proof is: If a line is tangent to a circle, then it is perpendicular to the point of tangency
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