Math 6A, Lesson 14, Spring 2018, 6/3/2018

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1. Perpendicular Bisectors and Angle Bisectors

  • Use of compass: center, radius, pin leg, and drawing leg
  • To draw a circle
  • To mark off or copy a line segment
  • How to draw a perpendicular bisector of a line segment?
  • Any point on the perpendicular bisector of a line segment is equidistant from the two  end points of the segment.

2. Angle Bisectors

  • A ray AZ divides <BAC into two equal angles, <BAZ and <CAZ. The ray is called the angle bisector of <ABC
  • How to draw an angle bisector?
  • Any point on the angle bisector of an angle is equidistant from the two sides of the angle.

3. Class work

  • Construct/draw circles, triangles, angles, equal line segments
  • construct /draw perpendicular bisectors of line segments
  • construct/draw angle bisectors of angles

4. Classification of Triangles

  • The number of equal sides in the triangle: scalene triangle – no equal sides; isosceles triangle – two equal sides; equilateral triangles – three equal sides
  • The type of angles of the triangle: acute-angled triangle – all angles are acute; right-angled triangle – one of the angles is a right angle; obtuse-angled triangle – one of the angles is an obtuse angle
  • Is an equilateral triangle also an isosceles triangle?
  • Is it Possible to draw a triangle with more than one obtuse angle?
  • Can a scalene triangle be an acute-angled, right-angled or obtuse-angled triangle?
  • All the three angles in a scalene triangle are different size
  • The angles opposite the equal sides of an isosceles triangle are equal
  • All the three angles in an equilateral triangle are equal in size

5. Quadrilaterals

  • A closed plane figure with four straight sides joined by four vertices is called a quadrilateral
  • Vertices, diagonals
  • Properties of special quadrilaterals
  • Parallelogram: 2 pairs of parallel and equal opposite sides
  • Rectangle: all angles are right angles
  • Rhombus: all sides are equal, diagonals are perpendicular to each other
  • Square: all sides are equal, all angles are right angles
  • Trapezoid: 1 pair of parallel sides

6. Home Work:

  • Handout:
    • Two pages
  • Workbook:
    • Page 48-50: 12, 13, 14,15,16

 

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