Shapes and Angles: Classification of angles

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This pdf covers, classifying angles on the basis of degree measurements for the proper understanding. Sample questions along with answers have also been provided.
1. Class Notes
Class - V Topic - Chapter – 2
Subject - Mathematics Shapes And Angles
Classification of Angles
On the basis of degree measurements the angles are classified.
Acute angle – An angle whose measure is more than 00 and less
than 900 is called an acute angle.
Example - ∠CBA is an acute angle.
∠CBA = 600
Right angle – An angle whose measure is 900 is called a right angle.
Example – ∠AOB is a right angle.
∠AOB = 900
Obtuse angle – An angle whose measure is more than 900 and less
than 1800 is called an obtuse angle.
Example - ∠DOQ is an obtuse angle.
∠DOQ = 1200
2. Straight Angle – An angle whose measure is equal to 1800 is called
a straight angle.
Example - ∠XOY is a straight angle.
∠XOY = 1800
Reflex Angle – An angle whose measure is more than 1800 and less
than 3600 is called a reflex angle.
Example - ∠RST is a reflex angle.
∠RST = 2200
Complete Angle – An angle whose measure is equal to 3600 is
called a complete angle.
Example - One complete rotation around P R S
a point P makes 3600 angle.
Here ∠SPR = 3600
Combination of Angles
Complementary Angles – Two angles are complementary if their
sum is equal to 900.
Example - ∠ABC = 600 , ∠CBD = 300 A
Here ∠ABC + ∠CBD = 600 + 300 = 900 C
So ∠ABC and ∠CBD are Complementary
Angles. B D
3. Supplementary Angles – Two angles are supplementary if their
sum is equal to 1800.
Example - ∠BOA = 1200, ∠AOC = 600
Here ∠BOA + ∠AOC = 1200 + 600 = 1800
So ∠BOA and ∠AOC are Supplementary
Angles in Clock
There are 12 equal divisions in a clock
for each hour. We know that one
complete rotation makes 3600 angle.
So angle formed between any two
consecutive numbers in a clock is
= 12
= 300
• We can estimate the measure of angle formed by counting
the number of divisions between the hour hand and minute
hand multiply with 300.
• We take the shortest path to do it.
• We can also tell the type of angles formed.
Example - At 8 ‘o’ clock the there are 4 gaps of 300
So the angle formed = 4 x 300 = 1200
4. Questions For Practice
Q1. Write any 3 examples of 2D and 3D shapes.
Ans . 2 Dimensional Shapes – Square, Rectangle, Triangle
3 Dimensional Shapes – Cone, Sphere, Cube
Q2. Write the types of angles for the given measurement.
(a) 790 (b) 1900 (c) 2890 (d) 1430 (e) 3600 (f) 1800
Ans . (a) 790 - Acute angle (b) 1900 - Reflex Angle
(c) 2890 - Reflex Angle (d) 1430 - Obtuse Angle
(e) 3600 - Complete Angle (f) 1800 - Straight Angle
Q3. In the given figure write the names of
(a) all the angles formed.
(b) all the arms of the angles formed.
(c) vertex of the angles.
Ans. (a) All angles:- ∠DOC, ∠DOB, ∠DOA, ∠COB, ∠COA, ∠BOA
(b) All arms :- DO, CO, BO, OA (C) Vertex :- O
Q4. Look at the pictures given below and write the types of the
angle. (a) (b) (c)
Ans. (a) Acute Angle (b) Obtuse Angle (c) Right Angle
5. Q5. Look at the angles formed in the pictures given below and fill
the table with tickmark for the angles.
Q6. Look at the times in the clocks. Write the time and type of
angles formed.
6. Q7. Fill in the blanks.
(a) At _____and _____ times in the clock right angle forms.
Ans. 9 ‘o’ clock, 3 ‘o’ clock
(b) At ________time straight angle forms in the clock.
Ans. 6 ‘o’ clock
(c) Two right angles make a _____angle. Ans. Straight
(d) Quarter of a complete angle is _____angle. Ans. Right
(e) 6 of a straight angle = ______degree. Ans. 30
Q8. Count the the number of right angles and number of angles
more than right angles in the these names.
Name Number of Number of angles more
right angles. than right angles.
(a) REENA 8 2
(b) MEERA 8 3
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