13.2 Triangles and quadrilaterals part 1_1allr

• Wiskunde
• Middelbare school
• vwo
• Leerjaar 1

Which exercises/theory should I discuss on the board?

How many angles does a
triangle have?

1. 3
2. 4
3. 5
4. 6

How many sides does a
quadrilateral have?

1. 3
2. 4
3. 5
4. 6

Triangles and Quadrilaterals

A triangle has 3 angles and 3 sides.
A quadrilateral has 4 angles and 4 sides.
Some triangles and quadrilaterals have special properties and therefore have their own name.

Right-angled triangle

A triangle that has one angle that is a right angle is called a right-angled triangle

Isosceles triangle

A triangle that has 1 axis of symmetry is called an isosceles triangle.
Because it has reflection symmetry 2 sides are the same length and two angles are the same size.
The angles with the same size are called the
base angles, the other angle is called the
apex angle.
The axis of symmetry divides the isosceles
triangle into two right-angled triangles.

Equilateral triangle

A triangle that has 3 axes of symmetry is called an equilateral triangle.

All sides of an equilateral triangle are the same
length and all angles are the same size.

Each axis of symmetry divides the equilateral
triangle into two right-angled triangles.

Squares and Rectangles

A rectangle is a quadrilateral where all angles are 90 degrees.
A square is a quadrilateral where all angles are 90 degrees AND all sides are the same length.

Rhombus

A rhombus is a quadrilateral where all sides are the same length. Both diagonals are axes of symmetry.

Kite

A kite is a quadrilateral
where one of the diagonals
is an axis of symmetry.
It has two pairs of sides
that are the same length.

Parallelogram

A parallelogram is a quadrilateral where the opposite sides are parallel to each other and the the same length.
The opposite angles are also equal.
It has rotation symmetry
through 180 degrees.

What kind of triangle is triangle PQR?

What kind of triangle is triangle PQR?

1. Not a special triangle
2. Right-angled triangle
3. Isosceles triangle
4. Equilateral triangle

What kind of triangle is triangle PQR?

PQR has a right angle, therefore it is a
right-angled triangle.
PQR has one axis of symmetry, therefore
it is an isosceles triangle.

PQR is a right-angled, isosceles triangle.

Weektask

Make and correct 13.2, 13.3 and 13.4