Question

A pattern of triangular numbers is shown. The first is 1, the second is 3, the third is 6, and so on. The formula 0.5n2 + 0.5n can be used to find the nth triangular number. Is 50 a triangular number? Explain.

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Answer 1

50 is not a triangular number

Explanation:

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = 45

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 =55

The way to calculate triangle numbers is to add the corresponding number.

For example, 1 is a triangle 1 + 2 is a triangle 1 + 2 + 3 is a triangle so on and so forth.

Triangle numbers would be 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, and 91