Basic purpose of this lecture is to present on World of Triangles. A triangle is a 3-sided polygon. Every triangle has three sides and three angles. When added together, the three angles equal 180°. Acute Triangles is a triangle in which all three angles are less than 90°. An obtuse triangle is a triangle in which one of the angles is greater than 90°. A right triangle is triangle with an angle of 90°. here also briefly describe on Isosceles Triangle Theorem and Pythagorean Theorem.