The interior angles are those on the inside of the triangle.

Try this Drag the orange dots on each vertex
A,B or C to reshape the triangle. Notice that the interior angles always add to 180°

The interior angles of a triangle always add up to 180°. Because of this, only one of the angles can be 90° or more. In a right triangle, since one angle is always 90°, the other two must always add up to 90°

A triangle is simply a polygon that has 3 sides. See interior angles of a polygon for the properties of the interior angles of a polygon with any number of sides.

- The interior angles of a triangle always add up to 180°
- Because the interior angles always add to 180°, every angle must be less than 180°
- The bisectors of the three interior angles meet at a point, called the incenter, which is the center of the incircle of the triangle.

- Triangle definition
- Hypotenuse
- Triangle interior angles
- Triangle exterior angles
- Triangle exterior angle theorem
- Pythagorean Theorem
- Proof of the Pythagorean Theorem
- Pythagorean triples
- Triangle circumcircle
- Triangle incircle
- Triangle medians
- Triangle altitudes
- Midsegment of a triangle
- Triangle inequality
- Side / angle relationship

- Perimeter of a triangle
- Area of a triangle
- Heron's formula
- Area of an equilateral triangle
- Area by the "side angle side" method
- Area of a triangle with fixed perimeter

- Right triangle
- Isosceles triangle
- Scalene triangle
- Equilateral triangle
- Equiangular triangle
- Obtuse triangle
- Acute triangle
- 3-4-5 triangle
- 30-60-90 triangle
- 45-45-90 triangle

- Incenter of a triangle
- Circumcenter of a triangle
- Centroid of a triangle
- Orthocenter of a triangle
- Euler line

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