Geometry

 Angles 1 Year = 360 Days  (approximately) This is the time that it takes for the Earth to rotate around the Sun. 1 Turn = 360 Degrees = 4 Right Angles Half Turn = 180 Degrees = a Straight Angle PROTRACTOR :  the instrument that is used to draw and measure angles. Where 2 Straight Lines cross, Vertical Angles are equal The sum of  Supplementary angles is 180 degrees. (definition) The sum of Complementary angels is 90 degrees. (definition) An acute angle is < 90 degrees. An Obtuse angle is > than 90 degrees, but less than 180 degrees 90 degrees < Obtuse angle < 180 degrees. Parallel Lines (Geometry Part 1, Unit 2, Lesson 6) Corresponding Angles are equal Alternate Interior Angles are equal Same-side Interior angles (or Co-interior angles) are Supplementary Exercises-Text: page 132 Triangles The sum of the internal angles of a triangle = 180 degrees. The EXTERIOR ANGLE of a triangle = the sum of the two interior opposite angles. Equilateral Triangle - all sides are equal. Isosceles Triangle - two sides are equal. Right Triangle - has one Right Angle. Quadrilaterals  Rectangle Parallelogram Rhombus Kite Trapezium Circles A point that moves so that it is always at a fixed distance (its radius) from a fixed point (its center), traces out a circle. The angle at the center of a circle = 360 degrees. Diameter = radius + radius = 2.radius The angle at the center of a circle is twice the angle at its circumference. The angle on a diameter = 90 degrees. Polygons A regular Polygon has all its sides equal. To find the sum of the interior angles of a Polygon,  divide the polygon into triangles and count how many there are, then multiply the number of triangles by 180 degrees. The sum of the External Angles of a Polygon = 360 Degrees. Names: 3 sides  -  Triangle 4 sides -  Quadrilateral 5 sides -  Pentagon 6 sides -  Hexagon 7 sides -  Heptagon 8 sides -  Octagon