###### Answer: c. 23.7 in.

In geometry an equilateral triangle is a triangle in which all three sides have the same length. In the familiar Euclidean geometry an equilateral triangle is also equiangular; that is all three internal angles are also congruent to each other and are each 60 °. It is also a regular polygon so it is also referred to as a regular triangle

Law of sines – Wikipedia

Law of sines – Wikipedia

Law of sines – Wikipedia

Law of sines – Wikipedia

In trigonometry the law of sines sine law sine formula or sine rule is an equation relating the lengths of the sides of a triangle (any shape) to the sines of its angles . According to the law = = = where a b and c are the lengths of the sides of a triangle and A B and C are the opposite angles (see the figure to the right) while R is the radius of the triangle s …

The angles in a triangle add up to 180° so 5α = 180 giving α = 36°. So the angles of the golden triangle are thus 36°-72°-72°. The angles of the remaining obtuse isosceles triangle …