
Concept explainers
(a)
Find the next 5 triangular numbers.
(a)

Answer to Problem 3CYU
The next 5 triangular numbers:
The next 5 triangular numbers:
Explanation of Solution
Given:
A number is triangular if it can be represented visually by a triangular array.
The first triangular number is 1. Find the next 5 triangular numbers.
Concept Used:
The first
Calculation:
The first triangle has just 1
The second triangle has another row with 2 extra dots, making 1+ 2 = 3
The third triangle has another row with 3 extra dots, making 1 + 2 + 3 = 6
The forth triangle has another row with 4 extra dots, making 1 + 2 + 3 +4 = 10
The fifth triangle has another row with 5 extra dots, making 1 + 2 + 3 + 4 +5 = 15
The fifth triangle has another row with 6 extra dots, making 1 + 2 + 3 + 4 +5 + 6 = 21
Thus, the next 5 triangular numbers:
(b)
Write a formula for the nth Triangular number.
(b)

Answer to Problem 3CYU
The nth Triangular number is the nth term of the natural number:
Explanation of Solution
Given:
A number is triangular if it can be represented visually by a triangular array.
Write a formula for the nth Triangular number.
Concept Used:
The nth Triangular number is the nth term of the natural number:
Thus, the nth Triangular number is the nth term of the natural number:
(c)
Prove that the sum of the first n triangular numbers equals
(c)

Explanation of Solution
Given:
A number is triangular if it can be represented visually by a triangular array.
Prove that the sum of the first n triangular numbers equals
Concept Used:
The nth Triangular number is the nth term of the natural number:
Calculation:
The nth Triangular number is the nth term of the natural number:
Sum of the first n triangular numbers =
Thus, the sum of the first n triangular numbers equals
Chapter 10 Solutions
Glencoe Algebra 2 Student Edition C2014
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