GIVEN: Sides of triangular field = 18 m, 80 m and 82 m CONCEPT: area of a triangular park = 5√3 × the area of a triangular field FORMULAE USED: Area of an equilateral triangle = (√3/4) a2 Area of triangle with sides a, b, and c = √[s(s - a)(s - b)(s - c)], where s = (a + b + c)/2 CALCULATION: s = (18 + 80 + 82)/2 = 90 The area of a triangular field = √[90(90 - 18)(90 - 80)(90 - 82)] = √[90 × 72 × 10 × 8] =720 m2 According to question, (√3/4) a2 = 5√3 × 720 a = 120 ∴ side of the triangular park = 120 m