**Chapter Notes and Summary**

• **Length : **distance between two end points of a line segment is called its length.•

**Protractor :**It is an instrument used for measuring or constructing an angle.

**figure formed by two rays with same initial point is called an angle and it is measured in degree**

Angle :

Angle :

**(°)**

**•**

**Right angle :**A quarter turn of one revolution by a ray is called a right angle i.e., 1 right angle = 90°.

**An angle whose measure is more than 0° but less than 90° is called an acute angle.**

(i) Acute angle :

(i) Acute angle :

**An angle whose measure is more than 90° but less than 180° is called an obtuse angle.**

(ii) Obtuse angle :

(ii) Obtuse angle :

**An angle whose measure is 180°, is called a straight angle.**

(iii) Straight angle :

(iii) Straight angle :

**An angle whose measure is more than 180° but less than 360° is called a reflex angle.**

(iv) Reflex angle :

(iv) Reflex angle :

**An angle whose measure is 360°, is called a complete angle.**

(v) Complete angle :

(v) Complete angle :

**•**

**Polygon :**A closed figure bounded by three or more than three line segments is called a polygon.

**• If a polygon is bounded by 3 sides, it is called a triangle.**

**• If a polygon is bounded by 4 sides, it is called a quadrilateral.**

**•**

**Triangle :**A plane figure bounded by three line segments is called a triangle and sum of angles of a triangle

**is 180°.**

**• If in a triangle each angle is acute, it is called an acute angled triangle.**

**• If in a triangle one angle is right angle, it is called a right angled triangle.**

**• If in a triangle, one angle is obtuse, it is called an obtuse angled triangle.**

**• A triangle having all three sides unequal is called a ‘scalene triangle.’**

**• A triangle having two sides equal is called an ‘isosceles triangle.’**

**• A triangle having all three sides equal is called an ‘equilateral triangle.’**

**•**

**Quadrilateral :**A plane figure bounded by four line segments is called a quadrilateral.

**• A quadrilateral having opposite pair of sides parallel is called a parallelogram.**

**• A quadrilateral having only one pair of parallel sides is called a trapezium.**

**• A quadrilateral having opposite sides equal and each angle of 90° is called rectangle.**

**• If a quadrilateral is having all sides equal and each angle of 90°, it is called a square.**

**• A parallelogram having all of its sides equal is called a rhombus.**

**•**

**Three dimensional shape :**

•

**Sphere :**An object which is in shape of a ball. It has a curved surface but no vertex and no edge.

**•**

**Cone :**Objects in form of ice-cream cone, a conical tent, birthday cap etc.

**•**

**Cylinder :**A circular pipe, a circular pillar etc. are in shape of cylinder. It has one curved surface and two

**circular faces at its ends.**

**•**

**Cuboid :**A brick, a matchbox, a book, etc. are in shape of a cuboid. It has length, breadth and height. It has

**6 rectangular faces. Two faces meet of a line segment called an edge. Three edges meet at a point called vertex.**

**•**

**Cube :**A cuboid whose length breadth and height are equal e.g., dice, ice cubes etc. A cube has 6 square faces,

**12 edges and 8 vertices.**

**•**

**Pyramid :**A solid whose base in a plane rectilinear figure and whose side faces are triangles having a common

**vertex.**