Question

An isosceles triangle ABC with the base BC is inscribed into a circle. Find the measure of angles of it, if measure of arc BC=102°.

Answer 1

Answer:

The measures of the angles of ΔABC are

m∠A = 51° , m∠B = 64.5 , m∠C = 64.5°

Step-by-step explanation:

* Lets revise some facts in the circle

- The measure of the circle is 360°

- Equal chords intercept equal arcs

- The measure of an inscribed angle equals half the measure

 of the intercepted arc

* Lets solve the problem

- ΔABC is isosceles withe base BC

∴ AB = AC

- The vertex angle is A

∵ ∠A is an inscribed angle subtended by arc BC

∴ m∠A = 1/2 the measure of arc BC

∵ The measure of arc BC = 102° ⇒ given

∴ m∠A = 1/2(102) = 51°

- In ΔABC

∵ AB = AC ⇒ proved

∴ m∠B = m∠C ⇒ base angles of isosceles Δ

- The sum of the interior angles in any Δ = 180°

∵ m∠A = 51 ⇒ proved

∴ m∠B = m∠C = (180 - 51) ÷ 2 = 129 ÷ 2 = 64.5°

* The measures of the angles of ΔABC are

  m∠A = 51° , m∠B = 64.5° , m∠C = 64.5°

Answer 2

Answer:

25.5°, 25.5°, 129° and 51°, 64.5°, 64.5°

Step-by-step explanation:

if you read the problem carefully you will notice that there are actually 2 ways of solving this problem. the first is by looking at the arc as if it is across from angle A, while the second is so the arc is across from side BC and bisected by point A (because the triangle is isosceles).

first way:

102/2=51°=m∠A

180-51=129°=m∠B+m∠C

129/2=m∠B=m∠C=64.5°

answers: 64.5°, 64.5°, 51°

second way:

102/2=51

51/2=m∠B=m∠C=25.5°

180-51=129°=m∠A

answers: 25.5°, 25.5°, 129°

Hope this helps!:)