Math Planet
Math Planet: Pre Algebra: Angles and Parallel Lines
Explains angles and parallel lines through examples and a video lesson.
CK-12 Foundation
Ck 12: Interactive Geometry: 4.2 Theorems About Lines and Angles
Consider two parallel lines that are intersected by a transversal, and when it crosses the two others, many different angle pairs are formed. See the special properties of the angle pairs in this interactive.
Math Open Reference
Math Open Reference: Corresponding Angles
Learn about corresponding angles with this resource which offers detailed explanations and examples. Subjects covered include parallel and non-parallel cases. Links to related topics.
Math Open Reference
Math Open Reference: Alternate Interior Angles
Explore the triangle inequality theorem with this helpful reference tool. Provides a detailed definition and an interactive activity that enhances further explanation. Includes links to related topics.
Illustrative Mathematics
Illustrative Mathematics: G Srt Joining Two Midpoints of Sides of a Triangle
In this task, students must prove that angles and triangles are congruent and that a parallel line passes through the midpoints of two sides of the larger triangle. Aligns with G-SRT.B.4.
Illustrative Mathematics
Illustrative Mathematics: G Gpe.5 Triangles Inscribed in Circle
In this task, students use ideas about linear functions to determine when certain angles are right angles. They use the fact that two lines (if not vertical or horizontal) are perpendicular when their slopes are inverse reciprocals, as...
Illustrative Mathematics
Illustrative Mathematics: G Gpe a Midpoint Miracle
In this task, students are asked to draw a quadrilateral so that no two sides are congruent, no two angles are congruent, and no two sides are parallel. The task gives students the opportunity to prove that if we join the midpoints of a...