8. Find the sum of first 51 terms of an AP whose second and third terms are 14 and 18 respectively.
8. Find the sum of first 51 terms of an AP whose second and third terms are 14 and 18 respectively.
Harshit Singh , 4 Years ago
Grade 12th pass
10 grade maths> 8. Find the sum of first 51 terms of an A...
1 AnswersPawan Prajapati
Given that,
Second term, a2 = 14
Third term, a3 = 18
Common difference, d = a3−a2 = 18−14 = 4
a2 = a+d
14 = a+4
a = 10 = First term
Sum of n terms;
Sn = n/2 [2a + (n – 1)d]
S51 = 51/2 [2×10 (51-1) 4]
= 51/2 [2+(20)×4]
= 51 × 220/2
= 51 × 110
= 5610
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