Transcript Triangular Numbers

Triangular Numbers
Learn to identify and
describe triangular
numbers
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What do you think a
triangular number is?
Do you remember how Square Numbers looked like
squares?
Well Triangular Numbers look like triangles!
But we use dots to form the
shape of a triangle. . .
See ->
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Let’s Take a Closer Look at Some
Triangular Numbers . . .
On a piece of paper, draw what you think the next
one will look like.
Then turn to the person sitting next to you and see if
you agree with each other.
I got . . .
Did you get the
same?
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Can you see the Pattern?
1
3
6
10
So 1, 3, 6, and 10 are triangular numbers.
Turn to the person sitting next to you and
describe to one another what pattern you can
Remember to
see.
raise your
hand and
wait for your
turn first!
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Describing the Pattern of
Triangular Numbers
2 Rows
of dots
1+2=3
3 Rows
of dots
1+2+3=6
4 Rows
of dots
1 + 2 + 3 + 4 = 10
- So each time we are adding an extra number in the sequence
because we are adding an extra row.
- each time the highest extra number we add will be 1 higher
than the last highest number added. This is because there will
be an extra dot in the new row added.
See if you can work out the next triangular
numbers in the pattern. . .
1 + 2 + 3 + 4 = 10
1 + 2 + 3 + 4 + 5 = 15
1 + 2 + 3 + 4 + 5 + 6 = 21
1 + 2 + 3 + 4 + 5 + 6 + 7 = 28
Activity Time
By drawing dots, using counters or just using the
pattern rule by adding the number of rows each
time, explore and record on your sheet as many
triangular numbers as you can find.
You will be using the triangular numbers you find
for a game afterwards. The more you find the
better chance you have of winning.
GOOD LUCK!
Game Time
GAME INSTRUCTIONS
Get your triangular numbers ready for
triangular number bingo!
On the grid of 10 boxes you will need to fill out the
triangular numbers you found (one per box).
If you did not find 10 triangular numbers, you will now
need to randomly add the rest of the numbers to you
list at the bottom of the sheet to play
If you found more than 10 triangular numbers, you
can only choose 10 of them for your bingo card.
Numbers called will be between 1 -100 ONLY. If you discovered a triangular
number higher than 100, firstly WELL DONE, then let your teacher know.
Triangular Bingo
First person to cross out all
of their numbers, stand up
and call Bingo WINS!
15
1
91
45
66
3
6
78
45
28
10
55
36
That’s all of the triangular numbers
under 100. Well done to those who
found 10 or more triangular numbers!
Interesting Fact About Triangular
Numbers
Add two neighbouring triangular numbers what do you notice?
10
3
6
+
6
+
10
=
=
9
16
+
What’s special
about these
numbers?
15
= 25
Lesson Review
• Triangular numbers are found from a pattern of
dots that form a triangle.
• Some triangular numbers are: 1, 3, 6, 10, 15, 21,
28, 36, 45 . . . So on.
• By adding another row of dots and counting all
the dots we can find the next number of the
sequence.
• Every time you add a row, there will be an
extra dot in that new row.
• Adding two triangular numbers that sit next to
each other will equal a square number.
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