ABC is an equilateral triangle with circumcenter O. What is the ratio of AO+ BO+ CO to the perimeter of the triangle?

Respuesta :

The ratio of AO + BO + CO to the perimeter of the triangle is 1/√3

Since O is the circumcenter of the equilateral triangle ABC, OA = OB = OC = l.

Also, since the triangle is an equilateral triangle, its sides are equal. So, AB = BC = AC = a.

Since the base angles of the equilateral triangle are 60°, OA, OB and AB form an isosceles triangle with base angles 30° since OA and OB bisect the base angles.

So ∠AOB + ∠OAB + ∠OBA = 180°

∠AOB + 30° + 30° = 180°  (∠OAB = ∠OBA = 30°)

∠AOB + 60° = 180°

∠AOB = 180° - 60°

∠AOB = 120°

Using the sine rule in triangle AOB,

OA/sinOBA = AB/sinAOB

l/sin30° = a/sin120°

l = asin30°/sin120°

l = a × 1/2 ÷ √3/2

l = a/√3

Since AO = BO = CO = l,

AO + BO + CO = l + l + l

= 3l

= 3a/√3

Also the perimeter of the triangle P = AB + BC + AC. Since AB = BC = AC,

P = AB + BC + AC

= a + a + a

= 3a

So, the ratio of AO + BO + CO to the perimeter of the triangle is 3a/√3 ÷ 3a = 1/√3

Thus, the ratio of AO + BO + CO to the perimeter of the triangle is 1/√3

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