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Question

If the area of an equilateral triangle is given as $900 \text{ m}^2$, then what is its perimeter?

The correct answer is
$60\sqrt[4]{27}\text{ m}$

Equilateral Triangle Area Formula

The area ($A$) of an equilateral triangle with side length ($s$) is given by the formula:

$A = \frac{\sqrt{3}}{4} s^2$

Calculating Side Length from Area

We are given the area $A = 900 \text{ m}^2$. We can use the area formula to find the side length ($s$):

  1. Substitute the area into the formula:

    $900 = \frac{\sqrt{3}}{4} s^2$

  2. Rearrange the formula to solve for $s^2$:

    $s^2 = \frac{900 \times 4}{\sqrt{3}} = \frac{3600}{\sqrt{3}}$

  3. Rationalize the denominator:

    $s^2 = \frac{3600 \times \sqrt{3}}{\sqrt{3} \times \sqrt{3}} = \frac{3600 \sqrt{3}}{3} = 1200 \sqrt{3}$

  4. Solve for $s$ by taking the square root:

    $s = \sqrt{1200 \sqrt{3}} = \sqrt{1200} \times \sqrt{\sqrt{3}}$

    $s = \sqrt{400 \times 3} \times (3^{1/2})^{1/2} = 20\sqrt{3} \times 3^{1/4}$

    $s = 20 \times 3^{1/2} \times 3^{1/4} = 20 \times 3^{(1/2 + 1/4)} = 20 \times 3^{3/4}$

    $s = 20 \times \sqrt[4]{3^3} = 20 \sqrt[4]{27} \text{ m}$

Calculating Perimeter

The perimeter ($P$) of an equilateral triangle is $P = 3s$. Substitute the calculated side length:

$P = 3 \times (20 \sqrt[4]{27})$

$P = 60 \sqrt[4]{27} \text{ m}$

Final Answer

The calculated perimeter matches Option A.

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Important Questions from Mensuration 2D (Notes)

  1. Find the area of a quadrilateral ABCD whose area is twice the area of a triangle PQR. The sides of triangle PQR are in the ratio 4:5:6 and the perimeter of the triangle is 90 cm (use $\sqrt{7} = 2.6$).
  2. Find the area of a regular hexagon whose side measures $14\sqrt{3}$ cm.
  3. Find the perimeter of the semi-circle of radius 21 cm.
    $\left(\text{Take } \pi = \frac{22}{7}\right)$
  4. The length of a diagonal of a rectangular park is 25 meters, and that of one of its sides is 15 meters. Find the perimeter of the park.
  5. The difference between two parallel sides of a trapezium is 9 cm. The perpendicular distance between them is 52 cm. If the area of the trapezium is 988 \(cm^2\), find the lengths of the parallel sides (in cm).

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