4.8 Properties of Two-dimensional Shapes

Unit Goals

  • Students classify triangles and quadrilaterals based on the properties of their side lengths and angles, and learn about lines of symmetry in two-dimensional figures. They use their understanding of these attributes to solve problems, including problems involving perimeter and area.

Section A Goals

  • Classify triangles (including right triangles), parallelograms, rectangles, rhombuses, and squares based on the properties of their side lengths and angles.
  • Identify and draw lines of symmetry in two-dimensional figures.

Section B Goals

  • Solve problems involving unknown side lengths, perimeter, area, and angle measurements using the known attributes and properties of two-dimensional shapes.
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Glossary Entries

  • acute angle
    An angle that measures less than 90 degrees.
  • angle
    A figure made up of two rays that share the same endpoint.
  • common denominator
    The same denominator in two or more fractions. For instance, \(\frac{1}{4}\) and \(\frac{5}{4}\) have a common denominator.
  • composite number
    A whole number with more than 1 factor pair.
  • denominator
    The bottom part of a fraction that tells how many equal parts the whole was partitioned into.
  • dividend
    The number being divided. For example, when 37 is divided by 5, we call 37 the dividend. 
  • equivalent fractions
    Fractions that have the same size and describe the same point on the number line. For example, \(\frac{1}{2}\) and \(\frac{2}{4}\) are equivalent fractions.
  • factor pair of a whole number
    A pair of whole numbers that multiply to result in that number. For example, 5 and 4 are a factor pair of 20.
  • intersecting lines
    Lines that cross.
  • line

    A set of points that are arranged in a straight way and extend infinitely in opposite directions.

  • line of symmetry
    A line that divides a figure into two halves that match up exactly when the figure is folded along the line.
  • mixed number
    A number expressed as a whole number and a fraction less than 1. 
  • multiple of a number
    The result of multiplying that number by a whole number. For example, 18 is a multiple of 3, because it is a result of multiplying 3 by 6.
  • numerator

    The top part of a fraction that tells how many of the equal parts are being described.

  • obtuse angle
    An angle that measures greater than 90 degrees.
  • parallel lines
    Lines that never intersect.
  • perpendicular lines
    Lines that intersect creating right angles.
  • point

    A location along a line or in space.

  • prime number
    A whole number that is greater than 1 and has exactly one factor pair: the number itself and 1.
  • ray
    A line that ends at one point and goes on in the other direction.
  • remainder
    The number left over when we take away as many equal groups as we can from a number. 
  • right angle
    An angle with a measurement of 90 degrees.
  • right triangle
    A triangle with a 90 degree angle.
  • rounding

    A formal way to say which number a given number is closer to. For example, for 182, the number 180 is the closest multiple of ten and 200 is the closest multiple of a hundred. We can round 182 to 180 (if rounding to the nearest ten) or 200 (if rounding to the nearest hundred).

  • segment or line segment

    A part of a line with two endpoints.

  • straight angle
    An angle that measures 180 degrees.
  • symmetry
    A figure has symmetry if its parts can match up exactly when the figure is folded or rotated.
  • vertex
    The point where the two rays meet.