1. Each of the numbers 1 = 1, 3 = 1 + 2, 6 = 1+ 2+ 3, 10 = 1 + 2 + 3+4, ... represents the number of dots that can be arranged evenly in an equilateral triangle: This led the ancient Greeks to call a number triangular if it is the sum of consecutive integers, beginning with 1. Prove the following facts concerning triangular numbers: (a) A number is triangular if and only if it is of the form n(n + 1)/2 for some n > 1. (Pythagoras, circa 550 B.C.) (b) The integern is a triangular number if and only if 8n + 1 is a perfect square. (Plutarch, circa 100 A.D.) (c) The sum of any two consecutive triangular numbers is a perfect square. (Nicomachus, circa 100 A.D.) (d) If n is a triangular number, then so are 9n + 1, 25n + 3, and 49n + 6. (Euler, 1775) anouo thot in terms of the binomial coefficients,

Elementary Geometry For College Students, 7e
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Chapter2: Parallel Lines
Section2.5: Convex Polygons
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2.1  question 1 please 

1. Each of the numbers
1 = 1, 3 = 1 + 2, 6 = 1+ 2+ 3, 10 = 1 + 2 + 3+4, ...
represents the number of dots that can be arranged evenly in an equilateral triangle:
This led the ancient Greeks to call a number triangular if it is the sum of consecutive
integers, beginning with 1. Prove the following facts concerning triangular numbers:
(a) A number is triangular if and only if it is of the form n(n + 1)/2 for some n > 1.
(Pythagoras, circa 550 B.C.)
(b) The integern is a triangular number if and only if 8n + 1 is a perfect square. (Plutarch,
circa 100 A.D.)
(c) The sum of any two consecutive triangular numbers is a perfect square. (Nicomachus,
circa 100 A.D.)
(d) If n is a triangular number, then so are 9n + 1, 25n + 3, and 49n + 6. (Euler, 1775)
anouo thot in terms of the binomial coefficients,
Transcribed Image Text:1. Each of the numbers 1 = 1, 3 = 1 + 2, 6 = 1+ 2+ 3, 10 = 1 + 2 + 3+4, ... represents the number of dots that can be arranged evenly in an equilateral triangle: This led the ancient Greeks to call a number triangular if it is the sum of consecutive integers, beginning with 1. Prove the following facts concerning triangular numbers: (a) A number is triangular if and only if it is of the form n(n + 1)/2 for some n > 1. (Pythagoras, circa 550 B.C.) (b) The integern is a triangular number if and only if 8n + 1 is a perfect square. (Plutarch, circa 100 A.D.) (c) The sum of any two consecutive triangular numbers is a perfect square. (Nicomachus, circa 100 A.D.) (d) If n is a triangular number, then so are 9n + 1, 25n + 3, and 49n + 6. (Euler, 1775) anouo thot in terms of the binomial coefficients,
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