6th Grade Math Triangle Interior Angle Sum



Hypothosis, Demo of the why, and one practice probelm


Click here to see an awesome video 🙂


Practice finding the missing angle here:





right arrow  A triangle has three sides and three angles

SIDES can be measured in inches, feet, centimeters, etc.

right arrow   The three angles always add to 180°

ANGLES are ALWAYS measured in DEGREES °

Equilateral, Isosceles and Scalene, what are the SIDE LENGTHS?

There are three special names given to triangles depending on its sides.

These names that tell you how many sides (or angles) are EQUAL.

There can be 32 or no equal sides/angles:

Equilateral Triangle

Equilateral Triangle (EQUAL)

Three equal sides
Three equal angles, always 60°

Isosceles Triangle

Isosceles Triangle (Interesting)

Two equal sides
Two equal angles

Scalene Triangle

Scalene Triangle (SCARY)

No equal sides
No equal angles

What Type of Angle?

Triangles can also have names that tell you what type of angle is inside:

Acute Triangle

Acute Triangle  (Cute and Small)

All angles are less than 90°

Right Triangle

Right Triangle  (Just Right!)

Has a right angle (90°)

Obtuse Triangle

Obtuse Triangle  (Oh wow that’s big)

Has an angle more than 90°

Combining the Names

Sometimes a triangle will have two names, for example:

Right Isosceles Triangle

Right Isosceles Triangle

Has a right angle (90°), and also two equal sides and two equal angles.

Can you guess the measurement of the two equal angles?

More information and fun at  https://www.mathsisfun.com/triangle.html