Lesson · Grade 6 · Mathematics
Classifying Triangles by Sides and by Angles
- Grade 6
- Mathematics
- 1 min 12 s
- British Columbia
- BC6-MA-37
A triangle with sides of 3, 4 and 5 cm is measured step by step. No two sides are equal, so it is scalene, and its biggest angle is exactly 90°, so it is a right triangle. A card lists scalene, isosceles and equilateral, then acute, right and obtuse, each with a small triangle turned a different way. Turning the triangle until its right angle sits at the bottom shows its name stays the same, and the video ends on the recap: check the equal sides, then the biggest angle.
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In one sentence
The question this lesson answers
What kind of triangle is this?
We can name a triangle by its sides and by its angles.
Transcript
What the lesson says
What kind of triangle is this?
We can name a triangle by its sides and by its angles.
A scalene triangle has no equal sides.
An isosceles triangle has two equal sides.
An equilateral triangle has three equal sides.
Our triangle has sides of 3, 4 and 5 centimetres.
No two sides are equal, so it is scalene.
An acute triangle has all three angles less than 90 degrees.
A right triangle has one angle of 90 degrees.
An obtuse triangle has one angle more than 90 degrees.
Our angles are 90 degrees, about 53 degrees and about 37 degrees.
The biggest angle is 90 degrees, so it is a right triangle.
Turning a triangle does not change its name.
So this is a scalene right triangle.
To name any triangle, check its equal sides, then its biggest angle.
Curriculum
Where this fits
- British Columbia, Grade 6
Mathematics, Geometry and measurement: trianglesBC6-MA-37
Previous: Volume of a Rectangular PrismNext: Plotting Points in the First Quadrant
The outcomes and strands follow the British Columbia curriculum.
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