SOLUTION: the second term A.P is 1 and the fifth term is -11 find the sum of its first 10 term.

Algebra ->  Sequences-and-series -> SOLUTION: the second term A.P is 1 and the fifth term is -11 find the sum of its first 10 term.      Log On


   

Question 935770: the second term A.P is 1 and the fifth term is -11 find the sum of its first 10 term.
Answer by dkppathak(439) About Me  (Show Source):
You can put this solution on YOUR website!
the second term A.P is 1 and the fifth term is -11 find the sum of its first 10 term.
solution
a+d=1
a+4d=-11 by subtraction
-3d=12
d=-4 a-4=1 than a=5
AP will be as 5,1,-3.....
sum of 10 terms = n[2a+(n-1)d]/2
=10[10+9x(-4)]/2
=10[10-36]/2= 5x(-26)= -130
answer -130