Mechanical Engineering > Gate 2022 Set-1 > Quants
An equilateral triangle, a square and a circle have equal areas.What is the ratio of the perimeters of the equilateral triangle to square to circle?
A
3√3 ∢ 2 ∢ √πœ‹
B
√(3√3):2:√πœ‹
C
√(3√3):4:2√πœ‹
D
√(3√3):2:2√πœ‹

Correct : b

Formulas for Area and Perimeter:
β€’     Equilateral Triangle with side length s:
    Area (At) = (s2√3) / 4
    Perimeter (Pt) = 3s
β€’     Square with side length a:
    Area (As) = a2
    Perimeter (Ps) = 4a
β€’     Circle with radius r:
    Area (Ac) = πr2
    Perimeter (Pc) = 2πr
Express Side/Radius in terms of Area (A):
Since At = As = Ac = A:
β€’     For the equilateral triangle:
    A = (s2√3) / 4
    s2 = 4A / √3
    s = √(4A / √3) = 2√A / (31/4)
β€’     For the square:
    A = a2
    a = √A
β€’     For the circle:
    A = πr2
    r2 = A / π
    r = √(A / π) = √A / √π
Calculate Perimeters in terms of Area (A):
β€’     For the equilateral triangle (Pt):
    Pt = 3s = 3 × (2√A / 31/4) = 6√A / 31/4
    To simplify 6 / 31/4:
    6 / 31/4 = (2 × 3) / 31/4 = 2 × 31 - 1/4 = 2 × 33/4
    Note that 33/4 = (33)1/4 = 271/4 = √√27.     Also, √(3√3) = (3 × 31/2)1/2 = (33/2)1/2 = 33/4.
    So, Pt = 2√A × √(3√3)
β€’     For the square (Ps):
    Ps = 4a = 4√A
β€’     For the circle (Pc):
    Pc = 2πr = 2π × (√A / √π) = 2√A√π
Determine the Ratio of Perimeters:
Pt : Ps : Pc = (2√A × √(3√3)) : (4√A) : (2√A√π)
Divide all terms by 2√A (since A is a positive area, √A ≠ 0):
√(3√3) : 2 : √π

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