Maths (school) · Part 05
Angles and area
Angle rules, polygons, circles, area and volume.
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- Angle rulesAngles on a straight line add up to 180 degrees, angles around a point add up to 360 degrees, and angles in a triangle add up to 180 degrees.
- Angles in parallel linesWhen a line crosses two parallel lines, matching angles are equal. Alternate angles form a Z shape and are equal. Co-interior angles form a C shape and add to 180 degrees.
- Angles in polygonsThe interior angles of a polygon with n sides add up to (n - 2) x 180 degrees. The outside (exterior) angles always add up to 360 degrees.
- Area of 2D shapesThe amount of flat space inside a shape, measured in square units.
- CirclesThe circumference is the distance around a circle and the area is the space inside. Both use pi, which is about 3.14.
- Arcs and sectorsA sector is a slice of a circle, like a pizza wedge. An arc is the curved edge of that slice. Both are fractions of the whole circle.
- Volume of prisms and cylindersA prism has the same shape all the way through. Its volume is the area of the cross-section times the length.
- Circle theoremsRules about angles inside circles. One example: an angle drawn from the two ends of a diameter to any point on the circle is always 90 degrees.