About Lesson

Understanding elementary shapes


  • A triangle with three unequal sides is called a scalene triangle.

  • A triangle with two equal sides is called an isosceles triangle.

  • A triangle with all its three sides equal is called an equilateral triangle. 

  • A triangle with all the three sides acute angles is an acute angled triangle.

  • A triangle with one obtuse angle and two acute angles is called an obtuse angled triangle.

  • A triangle with one of its angles right angle.


  • A trapezium is a quadrilateral with exactly one pair of opposite sides parallel.

  • A parallelogram is quadrilateral with both pairs of opposite sides parallel and equal.

  • A rectangle is a parallelogram in which the adjacent sides are at right angles and it’s opposite sides are equal. It’s diagonals are bisects each other.

  • A rhombus is a parallelogram all of whose sides have the same length.

  • A square is a parallelogram all of whose sides have the same length and all of whose angles are right angles.

  • Polygons are simple closed figures that consist of line segments joined in turn, so that each line segment intersects exactly two other line segments at their endpoints.

  • In polygon, the measure of each interior angle is less than 180°.Such a polygon is called convex polygon. If a polygon has at least one interior angle with a measure greater than 180°, the polygon is called a concave polygon.

  • A regular polygon is a polygon with all its sides and all its angles equal.