Triangle has three sides and three angles. The sum length of any two sides is longer than the length of the other side. All angles of a triangle always add up to 180 ̊C. Triangle has three types based on its three angles, including obtuse (1 angle > 90 ̊C), right (1 angle = 90 ̊C) and acute (no angle > 90 ̊C). It can be divided into three types based on three sides too, including scalene (no equal sides), equilateral (all sides equal) and isoscele (2 sides equal).

• Law of Cosines
a² = b² + c² - 2 × b × c × CosA;
b² = a² + c² - 2 × a × c × CosB;
c² = b² + a² - 2 × b × a × CosC;

• Area
a × b × Sin(C) / 2 or
c × b × Sin(A) / 2 or
a × c × Sin(B) / 2

• Angle Bisector of Side a
2 × b × c × Cos(A/2) / (b + c)

• Angle Bisector of Side b
2 × a × c × Cos(B/2) / (a + c)

• Angle Bisector of Side c
2 × a × b × Cos(C/2) / (a + b)

• Median of Side a ( m_a )
m_a² = (2 * b² + 2 * c² - a²) / 4

• Median of Side b ( m_b )
m_b² = (2 * a² + 2 * c² - b²) / 4

• Median of Side c ( m_c )
m_c² = (2 * a² + 2 * b² - c²) / 4

• Circumscribed Circle Radius
a / ( 2 * sin (A)) or
b / ( 2 * sin (B)) or
c / ( 2 * sin (C))

• Inscribed Circle Radius
a × Sin(C/2) × Sin(B/2) / Cos (A/2) or
b × Sin(A/2) × Sin(C/2) / Cos (B/2) or
c × Sin(A/2) × Sin(B/2) / Cos (C/2)