Math, asked by anyedina, 9 months ago

How will you guide children to find out which triangular number is equal to 120?

Answers

Answered by Anonymous

Answer:

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80+20+20=120

Answered by hrn21agmailcom

120

if €n is a triangular number

then €n = sum of preceding numbers from 1

given : €n = 120

means...

€n = n ( n + 1 ) /2 = 120

n ( n + 1 ) = 240

n^2 + n - 240 = 0

solving this QE...we get

n = 15

hence....

15th triangular number = 120

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