options: Prove theorems about triangles. Theorems include: measures of interior angles of a triangle sum to 180°; base angles of isosceles triangles are congruent; the segment joining midpoints of two sides of a triangle is parallel to the third side and half the length; the medians of a triangle meet at a point.

Prove theorems about lines and angles. Theorems include: vertical angles are congruent; when a transversal crosses parallel lines, alternate interior angles are congruent and corresponding angles are congruent; points on a perpendicular bisector of a line segment are exactly those equidistant from the segment’s endpoints.

Prove theorems about parallelograms. Theorems include: opposite sides are congruent, opposite angles are congruent, the diagonals of a parallelogram bisect each other, and conversely, rectangles are parallelograms with congruent diagonals.
problem_activity: Problem 1
Find all the angle measures that equal 127° and all the angle measures that are supplementary to 127°.
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Problem 2
In the figure,
$${\overline{AB} \parallel \overline{CD}}$$
and
$${\overline{EF} \parallel \overline{GH}}$$
. Prove that
$${\angle AFE \cong \angle DKH}$$
.
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correct_option_index: 1