triangle quadrilateral

7/31/2019 Triangle Quadrilateral

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Year 7 Triangles

I can identify and use geometricproperties of triangles to solve

problems.


2/17

Labelling lines and angles in a triangle

When we label angles in a triangle we use capital letters to label the vertices, going

round in order, clockwise or anticlockwise.

A

BC

a

b c

This triangle can be described as ABC.

The side opposite A is called side a.

The side opposite B is called side b.

The side opposite C is called side c.


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Labelling lines and angles in a triangle

How can we complete the labeling of this triangle?

?

? ?

r

This triangle is called PQR

P

q

Q

R p


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Right-angled triangle

Triangles are named according to their properties.

A right-angled triangle contains a right angle.

The longest side opposite the right angle

is called the hypotenuse.


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Isosceles triangle


An isosceles triangle has two equal sides.

Lines of symmetry are

indicated with dotted lines.

The two base angles are also equal.

An isosceles triangle has one line of symmetry.

The equal sides are indicated

by these lines.


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Equilateral triangle


An equilateral triangle has three equal sides

An equilateral triangle has three lines of symmetry

and has rotational symmetry of order 3.

and three equal angles.


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Scalene triangle


A scalene triangle has no equal sides and no equal angles.

A scalene triangle does not have any lines of symmetry.


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What type of triangle is this?

This is a right-angled isosceles

triangle.

It has one line of symmetry and no rotational symmetry.

Naming triangles

What symmetry properties does it have?


9/17

Triangles on a 3 by 3 pegboard


10/17

How to construct a triangle using 3 different methods

This will involve strengthening your knowledge and

understanding of how to use a compass and a

protractor.


11/17

1. Draw a line approximately 4cm Long and label it AB

4cmA B

2. Set your compasses to 5cm and with the point on A,scribe an arc above the line AB.

3. Set your compasses to 3cm and withthe point on B, scribe an arc above the

line AB. Where it crosses the other arc,call this point C

C

4. Draw the lines from A to C and B to Cto complete the construction.

3cm

Note this is a special type oftriangle. Measure angle B tofind out.

Side, Side, Side


12/17


4cmA B

3. Place the protractor on the line so that the cross-hairsare over point A and the 0 180

oline is covering the 4 cm

line. Then mark a point at 50o

2. Set the compasses to 5cm and with the compass point

at A, scribe an arc above the line AB

Side, Side, Angle


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3. Remove the protractor and draw a line from A to thepoint you have just marked at 500 through the arc. Callthis point C

4cmA B

C

4. Draw a line from point B to point C

50o

5cm

Side, Side, Angle


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4cmA B

2. Place the protractor on the line so that the cross-hairsare over point A and the 0 180

oline is covering the 4 cm

line. Then mark a point at 50oin an anticlockwise direction

Side, Angle, Angle


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4cmA B

2. Place the protractor on the line so that the cross-hairs

are over point A and the 0

180o

line is covering the 4 cmline. Then mark a point at 50

oin an anticlockwise direction

3. From A draw a line to the mark just made and mark theangle as 50

o

4. Now place the protractor on the line so that the cross-

hairs are over point B and the 0

180

o

line is covering the4 cm line. Then mark a point at 30oin a clockwise direction

50o

Side, Angle, Angle


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4cmA B

5. From B draw a line to the mark just made and mark theangle as 30

o

50o 30

o

6. Finally, where the two lines cross, mark that point C

C

Side, Side, Angle


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triangle quadrilateral

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