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| 1. |
Find the sum of 24 terms of the series 12- 22\xa0+ 32-42+52-62.......\xa0 |
| Answer» Series : (12-22) + (32-42) + (52-62) +....= (1-2) (1+2) + (3-4)(3+4) + (5-6)(5+6)+...= -3, -7, -11, .... forms an APa = -3 ; d = -7+3 = 4 ; n = 24Sn\xa0=\xa0\\({\\ n\\over 2 }\\)\\({ [2a+(n-1)d]}\\)= 12[ -6+23 X 4]12[ -6+ 92]= 12 X 86 = 1032 | |