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ICSE Class 10 Mathematics Question 19 of 49

Multiple-Choice Questions — Question 19

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Question 19

If the sum of n terms of an arithmetic progression Sn = n2 - n, then the third term of the series is :

  1. 2

  2. 4

  3. 6

  4. 9

Answer

Given,

Sum of n terms of an arithmetic progression Sn = n2 - n.

S1 = 12 - 1 = 0,

S2 = 22 - 2 = 4 - 2 = 2,

S3 = 32 - 3 = 9 - 3 = 6.

Sum upto first term = First term = 0.

Given, sum upto 2 terms = 2 and first term = 0, second term = 2.

Sum upto third term = 6

∴ First term + Second term + Third term = 6

⇒ 0 + 2 + Third term = 6

⇒ Third term = 6 - 2 = 4.

Hence, Option 2 is the correct option.