A triangle whose all the sides are unequal is called a scalene triangle.
A triangle, two of whose sides are equal in length is called an isosceles triangle.
A triangle, all of whose sides are equal is called an equilateral triangle.
A triangle, each of whose angles is less than 90°, is called an acute triangle.
A triangle with one of its angle 90° is called a right triangle.
A triangle with one of its angle greater than 90° is known as an obtuse triangle.
If a side of a triangle is produced, the exterior angle so formed is equal to the sum of two interior opposite angles.
∠x = ∠A + ∠B
∠A + ∠B + ∠C = 180° ....(1)
∠C + ∠x = 180° (linear pair) ....(2)
From (1) & (2)
∠x = ∠A + ∠B
