2 lines that are intersected by a third line known as a transversal.

2 intersecting lines, one of which is vertical and one of which is horizontal. The intersection forms…

Illustration used to prove the theorem "If three or more parallel lines intercept equal segments on…

Illustration of line segment AB, which is made up of line segments AC and CB. C is considered the midpoint…

"That point in which a right line drawn from the eye parallel to another given right line cuts the picture…

"Triclinic. Twinning very common, according to the albite law and evidenced by fine striation lines…

"Monoclinic. Crystals prismatic in habit; the prism faces make angles of 55 and 125 degrees with each…

"Monoclinic. Crystals prismatic in habit; the prism faces make angles of 55 and 125 degrees with each…

Tangrams, invented by the Chinese, are used to develop geometric thinking and spatial sense. Seven figures…

Tangrams, invented by the Chinese, are used to develop geometric thinking and spatial sense. Seven figures…

Tangrams, invented by the Chinese, are used to develop geometric thinking and spatial sense. Seven figures…

An illustration showing an angle the is less than a right angle. This is an acute angle.

An illustration showing the construction used to divide an angle into two equal parts. "With C as a…

An illustration showing the construction used to divide an angle into two equal parts when the lines…

Illustration used to show "The two perpendiculars to the sides of an angle from any point in its bisector…

Illustration used to show "The two perpendiculars to the sides of an angle from any point not in its…

An illustration showing a straight angle. When the sides of an angle extend in opposite directions,…

Illustration showing two positive angles; angle 1 being the acute angle and angle 2 being the reflex…

An illustration showing acute, obtuse, straight, right, and reflex angles.

An illustration of two angles that are adjacent. They have the same vertex and a common side between…

Angles 1 and 2 are adjacent angles. Two angles with a common vertex and a common side between them are…

Illustration showing that the difference between angle 1 and angle 2 is angle ABC.

An illustration showing an angle the is greater than a right angle and less than a straight angle. This…

Illustration showing four angles that can be used to define different relationships, such as adjacent,…