Big Ideas Math Integrated I, 2016
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Big Ideas Math Integrated I, 2016 View details
4. Equilateral and Isosceles Triangles
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Exercise 34 Page 614

a We already know that the angles of the triangular faces, and are congruent. Therefore, the vertex angle of which we have labeled below as , is congruent to

To find a second congruent angle, we have to consider the remaining angles of the triangular faces. Since and are both congruent and isosceles, their base angles will be the same.

Since the base angles are congruent, and they both sit on a straight line we know the following.
If we view as a transversal, we can identify and as alternate interior angles. According to the Alternate Interior Angles Theorem, if two parallel lines are cut by a transversal, then the pair of alternate interior angles are congruent.

This means we can also identify as congruent with

b Let's mark the distance in our diagram. Note that and therefore, we can mark as m since it's congruent corresponding side is .

In any isosceles triangle, the height bisects the base. Let's add this piece of information to the diagram.

As we can see, is half the base of each triangle. Therefore, the distance between the points and is