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Grade 6 · Math · Unit 11 of 18

Angles & Triangles

Measure, classify, find missing angles

What your child practises

Estimating and classifying angles (acute, right, obtuse, straight, reflex), finding missing angles on a line and in triangles, and classifying triangles by their sides and angles.

Prince Edward Island Curriculum curriculum outcome: SS1; SS2; SS4 · measuring and classifying angles, angle sums, and classifying triangles

How we explain it

Children can open this short lesson before they practise.

  1. Angles are measured in degrees. A right angle is 90°, a straight line is 180°.
  2. The three angles in any triangle add to 180°.
  3. Acute is under 90°. Obtuse is between 90° and 180°.

Example: A triangle has angles of 50° and 70°. What is the third angle? 50 + 70 = 120. 180 − 120 = 60. Answer: 60°

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    A triangle has sides of 10 cm, 10 cm and 11 cm. What type of triangle is it?

    • scalene
    • isosceles
    • equilateral

  2. Question 2

    Two angles together make a straight line. One of them is 42°. What is the other angle?

    answer box°

  3. Question 3

    This angle measures 180°. What kind of angle is it?

    • right
    • acute
    • straight
    • reflex
    • obtuse

  4. Question 4

    Two angles of a triangle are 94° and 48°. What is the third angle?

    answer box°

  5. Question 5

    Can a triangle have two right angles?

    • No, two right angles already add to 180°
    • Yes, but only if it is isosceles
    • Yes, if the third side is long enough
    • Only if it is equilateral

  6. Question 6

    About how many degrees is this angle?

    • 105°
    • 45°
    • 150°
    • 285°

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