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| 1. |
If Sn\xa0denotes the sum of first n terms of A.P. Prove that S30\xa0= 3(S20- S10). |
| Answer» 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 | |