13 Pri WB Math P5.pdf

8/14/2019 13 Pri WB Math P5.pdf

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Mathematics Pratomsuksa 5 Chapter 13 Exercises

124

Types of triangles

All triangles have 3 angles and 3 straight sides.

Shape Name Characteristics

1.

Equilateraltriangle

All sides of equal length Each angle 60 3 axes of symmetry

2.

Isoscelestriangle

2 sides of equal length Equal base angles 1 axis of symmetry

3. Scalenetriangle

All sides of different lengths All angles unequal

4. Acute-angledtriangle All angles acute

5.Obtuse-angled

triangle 1 obtuse angle

6.Right-angled

triangle 1 right angle

Base, base angles, vertex and height of triangle

Point P, point Qand point Rare the vertices.

h is the height.

QR is the base.

PQRand PRQare the base angles.

13 Tr iangles

13 Pri Edu WB Math P5.indd 124 2/17/11 9:43:27 AM


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Mathematics Pratomsuksa 5 Chapter 13 Notes

125

Drawing triangles

Always do a sketch of the triangle.

Draw it with a ruler, a compass and a protractor.

Interior angles of triangles

The total sum of the three interior angles of a triangle is 180.

a + b + c = 180

Perimeters of triangles

Perimeter =PQ+

QR+

RP

Areas of triangles

Area of a triangle =12

base height

Area of PQR =12

QR

QP

Area of STV =12

ST

UV



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126

A Name each triangle based on the characteristics of theangles and sides. Write the reason.

Triangle Name based on

angles Reason

Acute-angled triangleAll the angles areacute angles.

1.

Right-angled triangle One of the angles is aright angle.

2.Obtuse-angledtriangle

One of the angles isan obtuse angle.

3.

Acute-angled triangleAll the angles areacute angles.

Triangle Name based on sides Reason

Equilateral triangleAll the sides have thesame length.

4.Scalene triangle

All the sides havedifferent lengths.

5.Equilateral triangle

All the sides have thesame length.

6.

Isosceles triangle Two of the sides have

the same length.



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127

B Draw the axes of symmetry and ll in the blanks.

1.

No. of axis of symmetry: 1

2.


3.


4.


5.


6.




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128

C Fill in the blanks based on the given diagrams.

Triangle Base Base angle Vertex Height

Example:

YZ

XYZ andXZY

Point X,point Y

and point Z

XW

1.

UP

SUP andSPU

Point P,point S and

point U

SU

2.

NI LNI and

LIN

Point I,

point L andpoint N

LA

3.

NO

MNO andMON

Point M,point N

and pointO

MP

4.

MF

UFM andUMF

Point F,point M

and pointU

CU



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129

D Draw triangles based on these specications.

1. An equilateral triangle with sides of 4.0 cm each.

2. A XYZ withXZis 5 cm.

XYis 4 cm and

YZis 3 cm.

3. A RST withRSis 3 cm,

ST is 3 cm and RST is 90.

4. A MNO withMNis 5 cm, OMN and ONM are 45.



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131

3. The perimeter of an equilateral triangle is 45 centimeters. How long isthe side?

Answer:15 cm

H Calculate the areas of the given triangles.

1.

Area = 70square centimeters

2.


3.

Area = 24square meters

4.


5.


6.


I Answer the questions.

1. A triangle has a length of the base of 5 m and a height of 6 m. Whatis the area of the triangle?

Answer: 15 square meters



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132

2. What is the area of a triangle with the height of 2 m and the base ofthree times of its height?

Answer: 6 square meters

3. A triangular ag has a base of 30 cm and a height of 45 cm. It ismade up of a piece of paper. What is the total area of the paper?

Answer: 675 square centimeters

J Calculate the following. Show the working.

1. Find the area of ABCD, if AC is 10 cm.

Area of ABC =12

3 10

=15

Areaof ACD =12

3 10

=15

Areaof ABCD = 15 + 15 = 30 square centimeters

2. Ning wants to paint the board shown below. How many squarecentimeters does Ning need to paint?

Area of PRSU = 120 100

=12,000

Areaof UST =12 40 100

=2,000

Areaof PQR =12

40 100

=2,000

Total area = 12,000 + 2,000 + 2,000

= 16,000 square centimeters



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Mathematics Pratomsuksa 5 Chapter 13 Mastery Practice

133

1.

What is the name of thetriangle above?I Isosceles triangleII Equilateral triangleIII Acute-angled triangle

A I onlyB I and II onlyC II and III onlyD I, II and III

The base angles are the same. Two sides have the same

length.

2. Which of the following trianglesdoes the above informationdescribe?A Obtuse-angled triangleB Isosceles triangleC Scalene triangleD Right-angled triangle

3.

How many axes of symmetrydoes the above trianglehave?A 0 C 2B 1 D 3

4.

IfQSis the base, which is the

height of the triangle?

APQ C

PR

BRS D

PS

5. How many axes of symmetrydoes an equilateral trianglehave?A 0 C 2B 1 D 3

6.

Look at the above triangle.What is X?A 20 C 40B 30 D 50

7.

Study the above triangle. IfSRT = 30, STR =A 20 C 60B 40 D 90

M a s t e e r y P r a c t i c M a s t e e r y P r a c t i c



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Mathematics Pratomsuksa 5 Chapter 13 Mastery Practice

134

8. What is the value of an interiorangle of an equilateraltriangle?A 45 C 90

B 60 D 85

9.

What is the perimeter of theabove triangle?A 60 cm C 120 cm

B 40 cm D 150 cm

10. The perimeter of a triangularstamp is 7 cm. Its two similarsides are 2 cm each. What isthe length of its base?A 1 cm C 3 cmB 2 cm D 7 cm

11. A triangular cloth has 3 equalsides of 55 cm long. What isthe perimeter of the cloth?A 55 cm C 120 cmB 110 cm D 165 cm

12.

What is the area of the abovetriangle?A 3 square centimetersB 7 square centimetersC 6 square centimetersD 12 square centimeters

13.

Whatis the area of WXZ?

A 8 square meters

B 16 square meters

C 20 square meters

D 30 square meters

14.

Whatis the area of PQR?

A 35 square metersB 100 square meters

C 150 square meters

D 300 square meters

15. Calculate the area of a

triangle with the base of

30 cm and the height of a half

of the base.

A 15 square centimeters

B 30 square centimeters

C 225 square centimeters

D 450 square centimeters

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13 Pri WB Math P5.pdf