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The perpendicular distance of a chord 8 cm long from the centre of a circle of radius 5 cm is
  • a)
    2 cm
  • b)
    9 cm
  • c)
    4 cm
  • d)
    3 cm
Correct answer is option 'D'. Can you explain this answer?
Verified Answer
The perpendicular distance of a chord 8 cm long from the centre of a c...
Consider a circle having center O with a chord. Let OA be the radius of the circle and AB be the chord. As given in the question, the radius of the circle is 5 cm and length of chord is 8 cm. Let the distance between the center of the circle and chord be OP. So, this can be shown diagrammatically as:
It is clear from the diagram that OP is perpendicular to AB. As OP is perpendicular to AB and passes through the center O, it will bisect the chord AB at P. Now the length of AP will be,
AP =1/2 × AB
AP = 1/2 × 8
AP = 4 cm
Since, triangle OPA is a right-angle triangle, we can easily apply the Pythagoras theorem which can be stated as b2+p= h2 where b, p and h are base, perpendicular and hypotenuse of the respective triangle.
In ΔOPA,
AP2+OP2=AO2
OP= AO− AP2
OP2= 52−42
OP = 3 cm
Therefore, the distance of the chord AB from the center is 3 cm.
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Understanding the Problem
To find the perpendicular distance of a chord from the center of a circle, we can use the properties of triangles formed by the radius and the chord.
Given Information
- Length of the chord (AB) = 8 cm
- Radius of the circle (r) = 5 cm
Visualizing the Geometry
1. Draw a circle with center O and a chord AB.
2. Draw the perpendicular from O to AB, meeting it at point M (midpoint of AB).
3. OM is the perpendicular distance we need to find.
Breaking Down the Triangle
- Since M is the midpoint of AB, AM = MB = 4 cm (half of the chord).
- In triangle OMA, we can apply the Pythagorean theorem:
- OM^2 + AM^2 = OA^2
Where:
- OA = radius = 5 cm
- AM = 4 cm
Applying the Pythagorean Theorem
- Substitute the values:
- OM^2 + (4 cm)^2 = (5 cm)^2
- OM^2 + 16 = 25
- OM^2 = 25 - 16
- OM^2 = 9
- OM = √9 = 3 cm
Conclusion
Thus, the perpendicular distance of the chord from the center of the circle is:
3 cm
The correct answer is option 'D'.
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