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Question

From a point within an equilateral triangle, perpendicular lines are drawn to its sides. The lengths of these perpendiculars are 5 m, 6 m, and 7 m. Find the area of the triangle.

This question was previously asked in
RRB ALP 2025 CBT 2 Mechanic Motor Vehicle Question Paper (28-Jul-2026) (Shift 1)
The correct answer is
$108\sqrt{3}$ sq.m

Equilateral Triangle Altitude Calculation

For an equilateral triangle, the sum of the perpendicular distances from any interior point to its sides is equal to the triangle's altitude (\(h\)).

Given perpendicular lengths are 5 m, 6 m, and 7 m.

Therefore, the altitude \(h\) is:

\(h = 5 \, \text{m} + 6 \, \text{m} + 7 \, \text{m} = 18 \, \text{m}\)

Equilateral Triangle Side Length Derivation

The relationship between the altitude (\(h\)) and the side length (\(s\)) of an equilateral triangle is given by the formula:

\(h = \frac{\sqrt{3}}{2} s\)

Substitute the calculated altitude:

\(18 = \frac{\sqrt{3}}{2} s\)

Solve for \(s\):

\(s = \frac{2 \times 18}{\sqrt{3}} = \frac{36}{\sqrt{3}}\)

Rationalize the denominator:

\(s = \frac{36}{\sqrt{3}} \times \frac{\sqrt{3}}{\sqrt{3}} = \frac{36\sqrt{3}}{3} = 12\sqrt{3} \, \text{m}\)

Equilateral Triangle Area Calculation

The area (\(A\)) of an equilateral triangle with side length \(s\) is calculated using the formula:

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

Substitute the side length \(s = 12\sqrt{3}\) m:

\(A = \frac{\sqrt{3}}{4} (12\sqrt{3})^2\)

\(A = \frac{\sqrt{3}}{4} (144 \times 3)\)

\(A = \frac{\sqrt{3}}{4} \times 432\)

\(A = 108\sqrt{3} \, \text{sq.m}\)

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  2. In a workshop calculation, you need to find the side of a square base with an area of 64 cm2. What is the correct length?

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Important Questions from Mensuration

  1. In a circular garden of radius 15 m, a path of 2 m wide has to be made inside the garden at the rate of ₹ 24 per sq. m. The cost of making the path is: (Take π = \(\frac{22}{7}\) )

  2. A hollow cylinder with outer radius 4 cm and height 2 cm is made up of 1 cm thick metal sheet. What is the volume of metal used? (Take π = \(\frac{22}{7}\))

  3. The sides of a triangular park are 60 m, 297 m and 303 m. Its area is equal to the area of a square-shaped garden. What is the perimeter (in m) of the garden?

  4. The length and breadth of a rectangular field are in the ratio 4 : 3. If the cost of cultivating the field at 2 per m 2is 600, then the length of the field is:

  5. A cylindrical tank has a capacity of 5632 m3. If the diameter of its base is 8 m, what is the depth of the cylindrical tank? (Use π = \(\frac{22}{7}\))

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