Geometry and TrigonometryHardDistance from a circle's centre to a chord
Geometry and Trigonometry practice question
A circle with centre O has radius 10. Chord AB of the circle has length 12. What is the distance from O to chord AB?
Answer: 8
The perpendicular from O bisects the chord, giving a right triangle with hypotenuse 10 and leg 6: the distance is √(100 − 36) = 8.
Common wrong answers
- If you answered 2
- 2 subtracts the chord's half-length from 8.
- If you answered 4
- 4 subtracts 6 from 10.
- If you answered 6
- 6 is half the chord.
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