igsce maths directed numbers basics 1

1
directed numbers
basics a
2
in this lesson
we define directed numbers
we look at how we get directed numbers
we look at the importance of direction
3
what are directed numbers?
directed numbers are
positive (ve)
and negative (-ve)
numbers.
positive numbers
etc.
negative numbers
etc.
4
how we get directed numbers
5
where is the square,
the circle,
the triangle?
possible answers
triangle is to the left of square
circle is to the right of square
triangle is to the left of the circle
.
.
.
too many answers
we want one answer if possible
unique solution
6
where is the square,
the circle,
the triangle?
distance from the square of
the triangle
4 units to the left of the square
6 units to the right of the square
the circle
the square
0 units to the left or right of the square
7
where is the square,
the circle,
the triangle?
distance from the square of
4 units to the left of the square
-4
the triangle
the circle
6 units to the right of the square
6
the square
0
0 units to the left or right of the square
8
where is the square,
the circle,
the triangle?
3
6
0
5
7
8
9
-7
4
-1
-5
-6
1
2
-4
-2
-3
distance from the square of
-4
the triangle
the circle
6
the square
0
9
now back to our question
where is the square,
the circle,
the triangle?
3
6
0
5
7
8
9
-7
4
-1
-5
-6
1
2
-4
-2
-3
answer
the triangle is at
-4
better now only a few answers
the circle is at
6
0
the square is at
10
more about the distances
distances to the right are taken to be positive
ve
distances to the left are taken to be negative
-ve
11
choice of starting point
12
can we place zero elsewhere?
zero is arbitrary
yes
we choose where to place zero
can place zero here
can place zero here
zero is here
distance from the square of
the triangle is at
-4
the circle is at
we get the same distances in all cases
6
the square is at
0
13
positive numbers on the left?
14
where is the square,
the circle,
the triangle?
no
with positive on the left, do we get the same
distances?
with positive on the right
with positive on the left
the triangle is at
-4
the triangle is at
4
the circle is at
6
the circle is at
-6
0
0
the square is at
the square is at
we get different answers
not allowed or encouraged
15
can we place positive numbers on the left?
yes
but not allowed or encouraged
16
agreed facts 1
positive numbers should be on the right
on a number line
agreed facts 2
positive numbers can be written without sign
number number
12
12
we can clean our number line
this is our number line of choice
17
vertical number line
18
plane
6
bird
2
fish
-1
whale
-5
19
importance of direction
20
start
finish
he moved backward
distance moved -10
start
finish
distance moved 10
he moved forward
21
importance of direction
moving forward
distance moved is positive (ve)
moving backward
distance moved is negative (-ve)
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summary
positive/ negative numbers
we saw what directed numbers are
we saw how we get directed numbers
we saw the importance of direction
distance is taken to be positive
moving forward
distance is taken to be negative
moving backward
number number
12
12
very important!!!!
23
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