Question

Using alternate interior angles theorem, find $\angle a$ for the triangle in the image to be an equilateral triangle.
Given that the horizontal lines are parallel.

• A. ${75}^o$
• B. ${60}^o$

Answer 1

The correct option is B ${60}^o$

Equilateral triangles have an angle of ${60}^o$ each.

Also, the side AB is a transversal to the parallel lines.
$\therefore \angle a$ and $\angle b$ are alternate interior angles.
Also, $\angle a=\angle b$ (alternate interior angle theorem)
$\therefore \angle a={60}^o$