Question

select the best classification for the triangle by its angles. equiangular acute obtuse right

Explanation:

Step1: Recall angle - sum property of a triangle

The sum of interior angles of a triangle is $180^{\circ}$. One angle is given as $60^{\circ}$. Let the other two angles be $x$ and $y$. So $x + y+60^{\circ}=180^{\circ}$, which implies $x + y = 120^{\circ}$. Since the triangle has two equal - length sides (both 5.1), the angles opposite these sides are equal. Let $x = y$. Then $2x=120^{\circ}$, and $x = y = 60^{\circ}$.

Step2: Classify the triangle by angles

An equiangular triangle has all angles equal to $60^{\circ}$. Since all three angles of this triangle are $60^{\circ}$, it is an equiangular triangle.

Answer:

Equiangular