Triangular Numbers Worksheet
Explore geometric number patterns and visual additions
Name:
Date:
What is a Triangular Number?
A triangular number is a number that can be arranged in the shape of an equilateral triangle. Each step
adds a new row at the bottom with one more dot than the previous row!
Visual Pattern
Addition Expression
Total Number
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1
1
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1+2
3
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1+2+3
6
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1+2+3+4
10
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1+2+3+4+5
15
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1+2+3+4+5+6
21
Practice Exercises
Sequence: 1, 3, 6, 10, 15, 21,
1. Find the 7th Triangular Number:
,
Expression: 1 + 2 + 3 + 4 + 5 + 6 + 7 =
Answer:
2. Find the 8th Triangular Number:
Expression: 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 =
Answer:
★ Bonus Challenge!
Can you find the 10th triangular number without drawing the dots?
Expression: 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 =
Answer: