Class 9th Important questions of lines, angles and triangles

Important questions for class 9th related to Lines, Angles and Triangles

Angle: An angle is the union of two non-collinear rays with a common initial point. 

             The two rays forming an angle are called the "Arms" of the angle and the common initial point is called the "Vertex" of the angle.

Types of Angles: 

(a) Right Angle- An angle whose measure is 90⁰ is called a right angle.

(b) Acute Angle- An angle whose measure is less than 90⁰ is called an acute angle.

(c) Obtuse Angle- An angle whose measure is more than 90⁰ but less than 180⁰ is called an obtuse angle.

(d) Straight Angle-  An angle whose measure is 180⁰ is called a  Straight angle.

(e) Reflex Angle-  An angle whose measure is more than  180⁰ is called a Reflex angle.

(f) Complementary Angle- An angle, the sum of whose measure is 90⁰ are called an complementary angle. 

 (g) Supplementary Angle-  Two angles, the sum of whose measures is 180⁰ are called the supplementary angle.

Lines: A geometrical straight line is a collection of points and extends endlessly in both the directions. A straight line drawn on a sheet of paper with the help of a ruler and a sharp pencil is an example of a geometrical straight line.

Triangles: A plane figure bounded by three lines in a plane is called a triangle.