Illustration of a circle used to prove "Any angle inscribed in a segment less than a semicircle is an obtuse angle."

Obtuse Angles Inscribed in Circle Proof

Illustration of a circle used to prove "Any angle inscribed in a segment less than a semicircle is an…

Illustration of a circle with a right angle inscribed in a semicircle.

Circle With Inscribed Right Angle in Semicircle

Illustration of a circle with a right angle inscribed in a semicircle.

Illustrations of a circle with segment, semicircle, sector, quadrant, and central angles drawn.

Circle with Segment, Semicircle, Sector, Quadrant, and Central Angle

Illustrations of a circle with segment, semicircle, sector, quadrant, and central angles drawn.

Circular design made by rotating circles about a fixed point. The radii of the smaller circles is equal to the distance between the point of rotation and the center of the circle. The circles meet in the center of the larger circle. The design is achieved by removing consecutive halves of the circles (semi-circles).

Circular Design

Circular design made by rotating circles about a fixed point. The radii of the smaller circles is equal…

Circular design made by rotating circles about a fixed point. The radii of the smaller circles is equal to the distance between the point of rotation and the center of the circle. The circles meet in the center of the larger circle. The design is achieved by removing consecutive halves of the circles (semi-circles).

Circular Design

Circular design made by rotating circles about a fixed point. The radii of the smaller circles is equal…

The Roman lunette panel is a semicircle typically found on door-head.

Roman Lunette Panel

The Roman lunette panel is a semicircle typically found on door-head.

Illustration of a how to construct a square equivalent to a given parallelogram.

Parallelogram Used to Construct Equivalent Square

Illustration of a how to construct a square equivalent to a given parallelogram.

"The outer edge is a semicircle, with center at 0, and is divided into 360 parts. Each division is one-half of one degree, and, for convenience, the degrees are numbered from 0 to 180 from both A and B." — Hallock, 1905

Protractor

"The outer edge is a semicircle, with center at 0, and is divided into 360 parts. Each division is one-half…

A protractor is a semicircular tool for measuring angles in degrees.

Protractor

A protractor is a semicircular tool for measuring angles in degrees.

A protractor indicating a measurement of 10 degrees.

Protractor, 10 Degrees

A protractor indicating a measurement of 10 degrees.

A protractor indicating a measurement of 10 degrees from the right side.

Protractor, 10 Degrees

A protractor indicating a measurement of 10 degrees from the right side.

A protractor indicating a measurement of 100 degrees.

Protractor, 100 Degrees

A protractor indicating a measurement of 100 degrees.

A protractor indicating a measurement of 100 degrees from the right side.

Protractor, 100 Degrees

A protractor indicating a measurement of 100 degrees from the right side.

A protractor indicating a measurement of 105 degrees.

Protractor, 105 Degrees

A protractor indicating a measurement of 105 degrees.

A protractor indicating a measurement of 105 degrees from the right side.

Protractor, 105 Degrees

A protractor indicating a measurement of 105 degrees from the right side.

A protractor indicating a measurement of 110 degrees.

Protractor, 110 Degrees

A protractor indicating a measurement of 110 degrees.

A protractor indicating a measurement of 110 degrees from the right side.

Protractor, 110 Degrees

A protractor indicating a measurement of 110 degrees from the right side.

A protractor indicating a measurement of 115 degrees.

Protractor, 115 Degrees

A protractor indicating a measurement of 115 degrees.

A protractor indicating a measurement of 115 degrees from the right side.

Protractor, 115 Degrees

A protractor indicating a measurement of 115 degrees from the right side.

A protractor with 120 and 60 degree suplementary angles indicated.

Protractor, 120 and 60 Degrees

A protractor with 120 and 60 degree suplementary angles indicated.

A protractor indicating a measurement of 120 degrees.

Protractor, 120 Degrees

A protractor indicating a measurement of 120 degrees.

A protractor indicating a measurement of 120 degrees from the right side.

Protractor, 120 Degrees

A protractor indicating a measurement of 120 degrees from the right side.

A protractor indicating a measurement of 125 degrees.

Protractor, 125 Degrees

A protractor indicating a measurement of 125 degrees.

A protractor indicating a measurement of 125 degrees from the right side.

Protractor, 125 Degrees

A protractor indicating a measurement of 125 degrees from the right side.

A protractor indicating a measurement of 130 degrees.

Protractor, 130 Degrees

A protractor indicating a measurement of 130 degrees.

A protractor indicating a measurement of 130 degrees from the right side.

Protractor, 130 Degrees

A protractor indicating a measurement of 130 degrees from the right side.

A protractor with 135 and 45 degree suplementary angles indicated.

Protractor, 135 and 45 Degrees

A protractor with 135 and 45 degree suplementary angles indicated.

A protractor indicating a measurement of 135 degrees.

Protractor, 135 Degrees

A protractor indicating a measurement of 135 degrees.

A protractor indicating a measurement of 135 degrees from the right side.

Protractor, 135 Degrees

A protractor indicating a measurement of 135 degrees from the right side.

A protractor indicating a measurement of 140 degrees.

Protractor, 140 Degrees

A protractor indicating a measurement of 140 degrees.

A protractor indicating a measurement of 140 degrees from the right side.

Protractor, 140 Degrees

A protractor indicating a measurement of 140 degrees from the right side.

A protractor indicating a measurement of 145 degrees.

Protractor, 145 Degrees

A protractor indicating a measurement of 145 degrees.

A protractor indicating a measurement of 145 degrees from the right side.

Protractor, 145 Degrees

A protractor indicating a measurement of 145 degrees from the right side.

A protractor indicating a measurement of 15 degrees.

Protractor, 15 Degrees

A protractor indicating a measurement of 15 degrees.

A protractor indicating a measurement of 15 degrees from the right side.

Protractor, 15 Degrees

A protractor indicating a measurement of 15 degrees from the right side.

A protractor with 150 and 30 degree suplementary angles indicated.

Protractor, 150 and 30 Degrees

A protractor with 150 and 30 degree suplementary angles indicated.

A protractor indicating a measurement of 150 degrees.

Protractor, 150 Degrees

A protractor indicating a measurement of 150 degrees.

A protractor indicating a measurement of 150 degrees from the right side.

Protractor, 150 Degrees

A protractor indicating a measurement of 150 degrees from the right side.

A protractor indicating a measurement of 155 degrees.

Protractor, 155 Degrees

A protractor indicating a measurement of 155 degrees.

A protractor indicating a measurement of 155 degrees from the right side.

Protractor, 155 Degrees

A protractor indicating a measurement of 155 degrees from the right side.

A protractor indicating a measurement of 160 degrees.

Protractor, 160 Degrees

A protractor indicating a measurement of 160 degrees.

A protractor indicating a measurement of 160 degrees from the right side.

Protractor, 160 Degrees

A protractor indicating a measurement of 160 degrees from the right side.

A protractor indicating a measurement of 165 degrees.

Protractor, 165 Degrees

A protractor indicating a measurement of 165 degrees.

A protractor indicating a measurement of 165 degrees from the right side.

Protractor, 165 Degrees

A protractor indicating a measurement of 165 degrees from the right side.

A protractor indicating a measurement of 170 degrees.

Protractor, 170 Degrees

A protractor indicating a measurement of 170 degrees.

A protractor indicating a measurement of 170 degrees from the right side.

Protractor, 170 Degrees

A protractor indicating a measurement of 170 degrees from the right side.

A protractor indicating a measurement of 175 degrees.

Protractor, 175 Degrees

A protractor indicating a measurement of 175 degrees.

A protractor indicating a measurement of 20 degrees.

Protractor, 20 Degrees

A protractor indicating a measurement of 20 degrees.

A protractor indicating a measurement of 20 degrees from the right side.

Protractor, 20 Degrees

A protractor indicating a measurement of 20 degrees from the right side.

A protractor indicating a measurement of 25 degrees.

Protractor, 25 Degrees

A protractor indicating a measurement of 25 degrees.

A protractor indicating a measurement of 25 degrees from the right side.

Protractor, 25 Degrees

A protractor indicating a measurement of 25 degrees from the right side.

A protractor with 30 and 150 degree suplementary angles indicated.

Protractor, 30 and 150 Degrees

A protractor with 30 and 150 degree suplementary angles indicated.

A protractor indicating a measurement of 30 degrees.

Protractor, 30 Degrees

A protractor indicating a measurement of 30 degrees.

A protractor indicating a measurement of 30 degrees from the right side.

Protractor, 30 Degrees

A protractor indicating a measurement of 30 degrees from the right side.

A protractor indicating a measurement of 35 degrees.

Protractor, 35 Degrees

A protractor indicating a measurement of 35 degrees.

A protractor indicating a measurement of 35 degrees from the right side.

Protractor, 35 Degrees

A protractor indicating a measurement of 35 degrees from the right side.

A protractor indicating a measurement of 40 degrees.

Protractor, 40 Degrees

A protractor indicating a measurement of 40 degrees.

A protractor indicating a measurement of 40 degrees from the right side.

Protractor, 40 Degrees

A protractor indicating a measurement of 40 degrees from the right side.

A protractor with 45 and 135 degree suplementary angles indicated.

Protractor, 45 and 135 Degrees

A protractor with 45 and 135 degree suplementary angles indicated.

A protractor indicating a measurement of 45 degrees.

Protractor, 45 Degrees

A protractor indicating a measurement of 45 degrees.