Geometry › Alternate interior angles

Teacher info
Congruent angles INSIDE parallel lines
CCSS.MATH.CONTENT.HSG.CO.C.9
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.

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Algebra
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The mathematics of lines, shapes, and angles. Essential stuff for describing the world around you.
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Lines and angles
Related angles
Combining angles
Adding and subtracting adjacent angles
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Complementary angles
Learn about complementary and supplementary angles
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Coterminal angles
What about angles bigger than 360 degrees?
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Vertical angles
Angles on opposite sides of intersecting lines
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Corresponding angles
Parallel lines form congruent angles in matching places
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Alternate interior angles
Congruent angles INSIDE parallel lines
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Alternate exterior angles
Congruent angles OUTSIDE parallel lines
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Triangles
Triangle congruence and similarity
Polygons and quadrilaterals
Area of polygons
The Pythagorean theorem
Circles, ellipses, and their areas
Angles in circles
Lines in circles
Volume
Surface area
Transformations
Geometric optics