Chapter 18--Plane Figures

Chapter 18: Plane Figures

Lesson 1: Polygons. Objective: To identify polygons and to classify polygons as regular or not regular.

Lesson 2: Classify Triangles. Objective: to classify triangles by the lengths of their sides and by the measures of their angles.

Lesson 3: Classify Quadrilaterals. Objective: To identify and classify quadrilaterals.

Lesson 4: Problem Solving Strategy: Draw a Diagram. Objective: To use the strategy Draw a diagram to solve problems.

Lesson 5: Circles. Objective: To draw and identify the parts of circles.

Vocabulary: right angle, acute angle, obtuse angle, square, rectangle, polygon, triangle, quadrilateral, pentagon, hexagon, octagon, regular polygon, equilateral triangle, isosceles triangle, scalene triangle, trapezoid, Venn diagram, circle, center, chord, diameter, radius, compass

right angle: an angle that measures 90 degrees

acute angle: an angle that measures greater than 0 degrees but less than 90 degrees

obtuse angle:  an angle that measures greater than 90 degrees but less than 180 degrees

square: a quadrilateral with 4 equal sides and 4 right angles

rectangle: a quadrilateral with opposite sides that are equal, and 4 right angles

polygon: a closed plane figure with straight sides

triangle:  a polygon with 3 sides

quadrilateral:  a polygon with 4 sides

pentagon:  a polygon with 5 sides

hexagon:  a polygon with 6 sides

octagon:  a polygon with 8 sides

regular polygon:  a polygon in which all sides have equal length and all angles have equal measure

equilateral triangle:  a triangle with 3 equal sides

isosceles triangle:  a triangle with 2 equal sides

scalene triangle:  a triangle with no equal sides

trapezoid:  a quadrilateral with exactly one pair of parallel sides

Venn Diagram:  a diagram that shows relationships among sets of things

circle:  a closed plane figure made up of points that are the same distance from the center

center:  a point inside a circle that is the same distance from each point on the circle

chord:  a line segment that has its endpoints on the circle

diameter:  a chord that passes through the center of the circle

radius:  a line segment with one endpoint at the center of the circle and the other endpoint on the circle

compass:  a tool used to construct circles


Our textbook website:


Some good practice websites: