Mathematics.

 Trigonometry(plane trigonometry)

Trigonometry is branch of mathematics which tells about sides and  angles of triangles.

Triangle 📐 is classified as three categories on the basis of sides

(1). Equilateral triangle 📐 :- A triangle 📐 whose three(all) sides are equal to each other. 

(2). Isosceles triangle 📐:- A triangle 📐 whose any two sides equal to each other.

(2). Scalene triangle 📐 :- A triangle whose all sides are unequal to each other.

📝 All Angle of equilateral triangle are also equal (60°).

📝 the angle opposite to the equal sides of an isosceles triangle 📐 are equal.

Triangle can also classified on the basis of their angles.(by comparing from right triangle)

It is of three types.

Acute triangle:- A 📐 whose all angle is less than 90° 

Obtuse triangle:- A 📐 whose any angle is greater than 90°

Right triangle :-A 📐 whose any angle is equal to 90°

📝 Obtuse triangle can only one angle that is greater than 90°.

📝 Right triangle can only one angle equal to 90°

          Because total sum of any angle of triangle 📐 is equal to 180° 

Some extra valuable angle of two sides(arm) which can be applied in triangle 📐

💥Stright angle:- An angle whose degree measurement is equal to 180°

💥 Reflex angle:-An angle whose degree measurement is greater than 180°

💥 Supplementary angle:-A sum of two angle is equal to 180°

💥 Complementary angle:- A sum of two angle is equal to 90°

Note:- a straight angle can't make triangle 📐 it ultimately convert into a straight line (collinear )For a triangle 📐 it need non collinear point for formation of any type of triangle.

(Theses all are only for plane (2-D) angle of triangle 📐. that's why here tells about plane angle.

For 3-D their are solid angle used in practice.)