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If the difference between areas of the c...

If the difference between areas of the circumcircle and the incircle of an equilateral triangle is `44 cm^(2)`, then the area of the triangle is (Take `pi = (22)/(7)`)

A

`28 cm^(2)`

B

`7sqrt(3) cm^(2)`

C

`14sqrt(3) cm^(2)`

D

`21 cm^(2)`

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we need to find the area of an equilateral triangle given the difference between the areas of its circumcircle and incircle is 44 cm². ### Step-by-Step Solution: 1. **Understand the relationship between the circumradius (R) and inradius (r) of an equilateral triangle:** For an equilateral triangle, the circumradius (R) and inradius (r) are related by the formula: \[ R = 2r \] This means the circumradius is twice the inradius. 2. **Calculate the areas of the circumcircle and incircle:** The area of the circumcircle is given by: \[ \text{Area of circumcircle} = \pi R^2 \] The area of the incircle is given by: \[ \text{Area of incircle} = \pi r^2 \] 3. **Set up the equation for the difference in areas:** The difference between the areas of the circumcircle and incircle is given as: \[ \text{Area of circumcircle} - \text{Area of incircle} = 44 \] Substituting the areas: \[ \pi R^2 - \pi r^2 = 44 \] Factoring out \(\pi\): \[ \pi (R^2 - r^2) = 44 \] 4. **Use the difference of squares:** Since \(R^2 - r^2\) can be expressed as: \[ R^2 - r^2 = (R - r)(R + r) \] And since \(R = 2r\): \[ R - r = 2r - r = r \] \[ R + r = 2r + r = 3r \] Therefore: \[ R^2 - r^2 = r \cdot 3r = 3r^2 \] 5. **Substitute back into the equation:** Now we have: \[ \pi (3r^2) = 44 \] Solving for \(r^2\): \[ 3r^2 = \frac{44}{\pi} \] Substituting \(\pi = \frac{22}{7}\): \[ 3r^2 = \frac{44 \times 7}{22} = 14 \] \[ r^2 = \frac{14}{3} \] 6. **Find the circumradius (R):** Since \(R = 2r\), we can find \(R^2\): \[ R^2 = (2r)^2 = 4r^2 = 4 \times \frac{14}{3} = \frac{56}{3} \] 7. **Calculate the area of the triangle:** The area \(A\) of an equilateral triangle can be calculated using the inradius \(r\): \[ A = \frac{1}{2} \times \text{perimeter} \times r \] The perimeter of an equilateral triangle with side length \(a\) is \(3a\), and the relationship between \(r\) and \(a\) is: \[ r = \frac{a \sqrt{3}}{6} \implies a = \frac{6r}{\sqrt{3}} = 2\sqrt{3}r \] The area can also be expressed as: \[ A = \frac{\sqrt{3}}{4} a^2 = \frac{\sqrt{3}}{4} (2\sqrt{3}r)^2 = \frac{\sqrt{3}}{4} \cdot 12r^2 = 3\sqrt{3}r^2 \] Substituting \(r^2 = \frac{14}{3}\): \[ A = 3\sqrt{3} \cdot \frac{14}{3} = 14\sqrt{3} \] ### Final Answer: The area of the triangle is \(14\sqrt{3} \, \text{cm}^2\).
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Knowledge Check

  • If the difference between areas of the circumcircle and the incircle of an equllateral triangle is 44 cm^(2) , then the area of the triangle is (Take pi = (22)/(7) )

    A
    `28 cm^(2)`
    B
    `7 sqrt3 cm^(2)`
    C
    `14 sqrt3 cm^(2)`
    D
    `21 cm^2`
  • The ratio of the areas of the circumcircle and the incircle of an equilateral triangle is

    A
    `2:1`
    B
    `4:1`
    C
    `8:1`
    D
    `3:2`
  • The height of an equilateral triangle is 6cm, then the area of the triangle is

    A
    `9sqrt(3)cm^(2)`
    B
    `3sqrt(3)cm^(2)`
    C
    `12sqrt(3)cm^(2)`
    D
    `17sqrt(3)cm^2`
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