Triangular numbers
A triangular number is a number of dots that can be laid out as a triangle with rows of 1, 2, 3 and so on: 1, 3, 6, 10, 15 ... Two copies of a triangle make a rectangle, so 1 + 2 + ... + 100 is 100 × 101 ÷ 2 = 5,050, and two neighbouring triangular numbers make a square.
Depth 1 · Foundation
You can build triangular numbers as stairs of dots, find the next one by adding the next counting number, use two triangles that make a rectangle to add 1 to 100 quickly, and see two neighbours make a square.
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- 1
Foundation
You can build triangular numbers as stairs of dots, find the next one by adding the next counting number, use two triangles that make a rectangle to add 1 to 100 quickly, and see two neighbours make a square.
Your path here
What's still between you and Triangular numbers, depth 1, in the order you can learn it.
- 1CountingDepth 1 · Foundation · Number Systems
- 2Natural numbersDepth 1 · Foundation · Number Systems
- 3ZeroDepth 1 · Foundation · Number Systems
- 4The number lineDepth 1 · Foundation · Number Systems
- 5AdditionDepth 1 · Foundation · Arithmetic
- 6MultiplicationDepth 1 · Foundation · Arithmetic
- 7Square numbersDepth 1 · Foundation · Number Theory
- 8Triangular numbersDepth 1 · Foundation · Number Theory