Consider an arithmetic sequence whose common difference is 7 and sum of first 20 terms is 1530. write the algebraic expression of the sequence.
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Answer:
the sequence is 10, 17, 24, ............
the 20th term is 143
Step-by-step explanation:
d = 7
S20 = 1530
Sn = n/2 {2a+(n-1)d}
1530 = 20/2 {2a+(19)7}
1530 = 10 {2a+133}
153 = 2a + 133
153 - 133 = 2a
therefore,
a = 20/2
a = 10
let's try it out
S20 = 20/2{2(10)+(19)7}
= 10{20+133}
= 10{153}
= 1530
therefore, the required A.P. is
10,17,24.......
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