A triangle is a closed figure formed by three straight lines provided the sum of angles formed between the lines is 180 degrees. There are six types of triangles **• Isosceles Triangle:** A triangle with two sides of equal length and corresponding angles of equal measure. **Example:** Triangle with the angles 30°, 30° and 120°.

**• Equilateral Triangle:**A triangle that has all three sides of equal length and all three angles of equal measure. As the sum of the three angles must equal 180°, each angle equals 60° in an equilateral triangle.

**• Scalene Triangle:**If all the three sides of the triangle are of different size, then it is a scalene triangle.

**A triangle with sides 3cm, 4cm and 5cm is scalene.**

Example:

Example:

**• Right Triangle:**A triangle that has one 90° angle. • Acute Triangle: A triangle with all angles less than 90°.

**A triangle formed with angles 50°, 60° and 70° is an acute triangle**

Example:

Example:

**• Obtuse Triangle:**An obtuse triangle is a triangle with one angle greater than 90° o

**Example:**Triangle with angles 30°, 30° and 120°.

**Commonly used Terms**

**The perpendicular distance from the base to the opposite vertex.**

Altitude:

Altitude:

**We can take any side of the triangle as the base, for the purposes of further calculation.**

Base:

Base:

**Vertex:**Angles of triangles are called vertices.

Any one of AB, BC or AC could be taken as the base. In this case, AD is the Altitude, and BC is the base. Angle A, Angle B and Angle C...