Question:medium

If length of the tangent is \(8\) cm and the distance between the center of the circle and the external point is \(11\) cm, then the area of the circle is

Show Hint

For a tangent from an external point, use \(t^2=d^2-r^2\).
  • \(100\text{ cm}^2\)
  • \(197.14\text{ cm}^2\)
  • \(179.14\text{ cm}^2\)
  • \(110.14\text{ cm}^2\)
Show Solution

The Correct Option is C

Solution and Explanation

Step 1: Understanding the Concept:
The relationship between the radius of a circle, the length of a tangent from an external point, and the distance from that point to the center of the circle forms a right-angled triangle. We can use this property to find the radius and then calculate the area.
Step 2: Key Formula or Approach:
Let:
$r$ be the radius of the circle.
$L$ be the length of the tangent from the external point.
$d$ be the distance from the external point to the center.
These three lengths form a right-angled triangle with $d$ as the hypotenuse. The relation is given by the Pythagorean theorem: \[ r^2 + L^2 = d^2 \] The area of a circle is given by $A = \pi r^2$.
Step 3: Detailed Explanation:
We are given:
Length of the tangent, $L = 8$ cm.
Distance from the center, $d = 11$ cm.
Using the Pythagorean relation: \[ r^2 + 8^2 = 11^2 \] \[ r^2 + 64 = 121 \] Solve for $r^2$: \[ r^2 = 121 - 64 \] \[ r^2 = 57 \] Now, calculate the area of the circle: \[ A = \pi r^2 \] \[ A = 57\pi \] To find the numerical value, we can use the approximation $\pi \approx 3.14159$ or $\pi \approx 22/7$. Using $\pi \approx 22/7$: \[ A \approx 57 \times \frac{22}{7} = \frac{1254}{7} \approx 179.1428... \text{ cm}^2 \] Using $\pi \approx 3.14$: \[ A \approx 57 \times 3.14 = 178.98 \text{ cm}^2 \] Both approximations are very close to the value in option (C).
Step 4: Final Answer:
The area of the circle is $57\pi$ cm$^2$, which is approximately 179.14 cm$^2$. Therefore, option (C) is correct.
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