SOLUTION: Find the first term of an A.p if the 5th term is 28 and sum of the first 17th term is Zero

Question 858285: Find the first term of an A.p if the 5th term is 28 and sum of the first 17th term is Zero
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
Find the first term of an A.p if the 5th term is 28 and sum of the first 17th term is Zero
tn = a+(n-1)d
28 = a+4d
a+4d= 28....................(1)
Sn = n/2( 2a+(n-1)d))
0= (17/2)(2a+16d)
0= 17(2a+16d)
34a+272d=0
/34
a+8d=0.....................(2)
subtract (2) from (1)
we get -4d=28
d= -7
Now a+4d=28
a+4*(-7)=28
a-28=28
a=56

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