# त्रिकोणी संख्या

A triangular number is a number that can be represented as a sum of consecutive positive integers starting from

1. The formula to calculate the nth triangular number is Tn = (n(n+1))/2.

Here are the first ten triangular numbers:

T1 = 1

T2 = 3

T3 = 6

T4 = 10

T5 = 15

T6 = 21

T7 = 28

T8 = 36

T9 = 45

T10 = 55

1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 105, 120, 136, 153, 171, 190, 210, 231, 253, 276, 300, 325

Which of the following is a triangular number?

a. 9

b. 14

c. 21

d. 28

Answer: c. 21

What is the fourth triangular number?

a. 6

b. 10

c. 15

d. 21

Answer: b. 10

What is the 10th triangular number?

a. 45

b. 50

c. 55

d. 60

Answer: c. 55

Which of the following is not a triangular number?

a. 16

b. 21

c. 28

d. 36

Answer: a. 16

What is the difference between the 6th and 7th triangular numbers?

a. 6

b. 7

c. 8

d. 9

Answer: b. 7

Which of the following is the 15th triangular number?

a. 105

b. 120

c. 136

d. 153

Answer: b. 120

Which of the following is a triangular number that is also a perfect square?

a. 9

b. 16

c. 25

d. 36

Answer: c. 25

What is the next triangular number after 21?

a. 22

b. 24

c. 28

d. 30

Answer: b. 28

What is the 20th triangular number?

a. 190

b. 200

c. 210

d. 220

Answer: c. 210

What is the sum of the first 10 triangular numbers?

a. 385

b. 450

c. 505

d. 550

Answer: a. 385

What is the difference between the 11th and 12th triangular numbers?

a. 11

b. 12

c. 13

d. 14

Answer: b. 12

What is the 25th triangular number?

a. 300

b. 325

c. 350

d. 375

Answer: b. 325

Which of the following is the largest triangular number less than 100?

a. 45

b. 66

c. 78

d 91

Answer: d. 91

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