Sum of 7 terms of an AP is 49 and that of 17 terms is 289. Find the sum pf n terms of this AP.
No spam plz...only of you know the answer attempt.
Answers
Answered by
1
sn is equal to n*n and hope this help
Attachments:
maroon5:
Good answering you can become a genius some day... regards... cheers ✌✌
Answered by
2
S 7 = 7/2 [2a+(6)d]
49* 2/7 = 2a+6d
7*2 = 2a+6d
14 = 2a+6d........(1)
s17= 17/2 (2a+16d)
289*2/17 = 2a+16d
17*2 = 2a + 16d
34 = 2a + 16d .........(2)
subtracting eq. 2 from 1 we will get
20 = 10 d
so ,d = 2
putting d = 2 in eq. 1
14 = 2a + 6 * 2
14 = 2a + 12
14 - 12 = 2a
2a = 2
a = 1
sn= n/2 [2a+ (n-1)d]
=n/2[2(n)]
=n2
sn =n2
so sum of first natural number = n2
49* 2/7 = 2a+6d
7*2 = 2a+6d
14 = 2a+6d........(1)
s17= 17/2 (2a+16d)
289*2/17 = 2a+16d
17*2 = 2a + 16d
34 = 2a + 16d .........(2)
subtracting eq. 2 from 1 we will get
20 = 10 d
so ,d = 2
putting d = 2 in eq. 1
14 = 2a + 6 * 2
14 = 2a + 12
14 - 12 = 2a
2a = 2
a = 1
sn= n/2 [2a+ (n-1)d]
=n/2[2(n)]
=n2
sn =n2
so sum of first natural number = n2
I am giving BRAINLIEST to that guy because he has a lot of distance to reach the top level....but your answer was simple clear and sweet. Thank you....keep learning... keep helping ✌✌
it's ok
ur welcome
Similar questions