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17. In an AP the sum of first n terms is +3n2 13nFind the 25th term. |
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Answer» Sn = 3n²/2 + 5n/2 We know that , nth term = (sum of nth term) - (sum of (n-1)th term) So , according to the question , 25th term = (sum of 25th term) - (sum of (25-1)th term)= (sum of 25th term) - (sum of 24th term)= [3(25)²/2 + 5(25)/2] - [3(24)²/2 + 5(24)/2]= [1875/2 + 125/2] - [1728/2 + 120/2]= (2000/2) - (864 + 60)= 1000 - 924= 76 So , the 25th term of the AP is 76. |
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