3.17 Triangles

Mathematics

Space and shape

Educator section

Memorandum

22.3

(a) right-angled

(b) equilateral

(c) acute-angled

(d) isosceles

(e) obtuse-angled

22.4

(a) one obtuse angle

(b) 2 sides equally long

(c) 3 different lengths

(d) one angle 90°

Leaner section

Content

Activity: triangles [lo 3.1, lo 3.2, lo 3.4, lo 4.9]

22. TRIANGLES

22.1 Draw the triangles shown below on graph paper. Cut them out neatly. With a friend, sort these triangles into groups. The triangles in each group must have the same characteristics. Explain to the rest of the class why you sorted the triangles into these groups.

22.2 Did you know?

We can classify triangles according to their angles or their sides.

a) Acute-angled triangle

b) Right-angled triangle

c) Obtuse-angled triangle

d) Equilateral triangle

All three sides are equally long.

e) Scalene triangle

All three sides have different lengths.

f) Isosceles triangle

There are two equally long sides.

22.3 Identify the triangles shown below:

______________________________

b)

______________________________

c)

______________________________

______________________________

e)

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22.4 Now draw your own:

a) Obtuse-angled triangle

b) Isosceles triangle

c) Scalene triangle

d) Right-angled triangle

Assessment

Learning Outcome 3: The learner will be able to describe and represent characteristics and relationships between two-dimensional shapes and three-dimensional objects in a variety of orientations and positions.

Assessment Standard 3.1: We know this when the learner recognises, visualises and names geometric figures and solids in natural and cultural forms and geometric settings, including those previously dealt with.

Assessment Standard 3.2: We know this when the learner in contexts that include those that may be used to build awareness of social, cultural and environmental issues, describes and classifies geometric figures and solids in terms of properties;

Assessment Standard 3.4: We know this when the learner designs and uses nets to make models of geometric solids studied up to and including this grade;

Learning Outcome 4: The learner will be able to use appropriate measuring units, instruments and formulae in a variety of contexts.

Assessment Standard 4.9: We know this when the learner estimates, compares, measures and draws angles accurate to one degree using protractors.