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Grade 4 - Mathematics
4.2 Triangles

  • A triangle is a 3 sided polygon.
  • Triangles are two-dimensional figures.
  • Triangles can be classified according to the relative lengths of their sides as:
    • Equilateral triangle (3 sides of equal length)
    • Isosceles triangle (two sides are of equal length)
    • Scalene triangle (all sides have different lengths)
  • Triangles can also be classified according to the their internal angles as:
    • Right triangle (or right-angled triangle) has one 90° internal angle (a right angle). The side opposite to the right angle is the hypotenuse; it is the longest side in the right triangle. The other two sides are the legs of the triangle.
    • An obtuse triangle has one internal angle larger than 90° (an obtuse angle).
    • An acute triangle has internal angles that are all smaller than 90° (three acute angles).
    • An equilateral triangle is an acute triangle, but not all acute triangles are equilateral triangles.
    • An oblique triangle has only angles that are smaller or larger than 90°. It is therefore any triangle that is not a right triangle.
  • The angles of a triangle add up to 180 degrees.
  • The sum of the lengths of any two sides of a triangle always exceeds the length of the third side. That is called the triangle inequality.
Example: A triangle with one obtuse angle and two sides equal.
Answer: Acute Isosceles triangle

Directions: Read the questions carefully and identify the type of triangle. Also draw an acute, obtuse, right, scalene, isosceles, equilateral triangle and show its properties.
Q 1: I have a right angle and all my sides are different. What am I?
Scalene Acute Triangle
Acute Equilateral Triangle
Right Scalene Triangle
Right Isosceles Triangle

Q 2: An obtuse angle is
Greater than 90
Equal to 90
Less than 90

Q 3: I have an obtuse angle and 2 equal sides. What am I?
Obtuse Equilateral Triangle
Acute Isosceles Triangle
Right Scalene Triangle
Obtuse Isosceles Triangle

Q 4: A right angle is
less than 90
Equal to 90
Greater than 90

Q 5: An acute angle is
Equal to 90
Less than 90
Greater than 90

Q 6: I have all acute angles and 3 equal sides. What am I?
Scalene Right Triangle
Acute Scalene Triangle
Acute Equilateral Triangle
Scalene Obtuse Triangle

Q 7: I have 3 acute angles and 3 equal sides. What am I?
Right Equilateral Triangle
Obtuse Scalene Triangle
Acute Scalene Triangle
Acute Equilateral Triangle

Q 8: A figure that can be folded in half so that the 2 halves match is
a polygon

Question 9: This question is available to subscribers only!

Question 10: This question is available to subscribers only!

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