NCERT Exemplar Solutions
Class 10 - Mathematics - CHAPTER 11: Area Related To Circles - Exercise 11.2Question 7
Class 10 - Mathematics - CHAPTER 11: Area Related To Circles - Exercise 11.2
Question. 7
The numerical value of the area of a circle is greater than the numerical value of its circumference. Is this statement true? Why?
Answer:
Detailed Answer with Explanation:
Step 1: Recall the formulas
For a circle of radius \(r\) metres:
- Area = \(\pi r^2\) square metres (\(m^2\))
- Circumference = \(2\pi r\) metres (\(m\))
Step 2: Compare their numerical values
We are not comparing the units (since area and length are different quantities), but only the numbers that come in front of the units.
So, compare: \(\pi r^2\) (number from area) and \(2\pi r\) (number from circumference).
Step 3: Cancel common factor
Both expressions have \(\pi\). Divide both sides by \(\pi\):
Compare \(r^2\) with \(2r\).
Step 4: Simplify
Divide both sides by \(r\) (assuming \(r > 0\)):
Compare \(r\) with 2.
Step 5: Interpret
- If \(r > 2\) m → Area number > Circumference number
- If \(r = 2\) m → Area number = Circumference number
- If \(r < 2\) m → Area number < Circumference number
Step 6: Conclusion
The statement says “the area is greater than the circumference” as if it is always true. But it depends on the radius:
Only for radii greater than 2 m is the area number larger. For smaller radii, it is not.
Therefore, the statement is False.