**RS Aggarwal Solutions for Class 7, Chapter 15 are provided in geometry as "Properties of the Triangle". A triangle is a polygon that consists of three sides, three edges, three vertices and the sum of internal angles of a triangle equal to 180°. In the beginning, we start from understanding the shape of triangles, its types and properties, theorems based on it such as Pythagoras theorem, etc. The properties of the triangle are:**

- The sum of all the angles of a triangle (of all types) is equal to 180°.
- The sum of the length of two sides of a triangle is greater than the length of the third side.
- In the same way, the difference between the two sides of a triangle is less than the length of the third side.
- The side opposite the greater angle is the longest side of all the three sides of a triangle.
- The exterior angle of a triangle is always equal to the sum of the interior opposite angles. This property of a triangle is called an exterior angle property.
- Two triangles are said to be similar if their corresponding angles of both triangles are congruent, and lengths of their sides are proportional.
- Area of a triangle = ½ × Base × Height
- The perimeter of a triangle = sum of all its three sides.