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If Sn denotes the sum of first …

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If Sdenotes the sum of first n terms of A.P. Prove that S30 = 3(S20- S10).

  • 1 answers

Rashmi Bajpayee 7 years, 2 months ago

R.H.S.

3[20/2{2a + (20 - 1)d} - 10/2{2a + (10 - 1)d]

= 3[10{2a + 19d - 5{2a + 9d}]

= 15[4a + 38d - 2a - 9d]

= 30/2[2a + 29d]

= 30/2[2a + (30 - 1)d]

= S30

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