If the sum of first 9 terms of an Ap is 72 and the common difference is 5 find the first term and the 10th term
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Answered by
18
Answer:
a=-12, t(10) =33
Step-by-step explanation:
Given
sum of the first 9 terms of an A. P = 72
S(9)=72
d=5
To find:
a=?
t(10)=?
solve:
S(9)=72
S(n) =n/2 {2a+(n-1) d}
s(9)=9/2{2a+(9-1)5}
72=9/2{2a+(8)5}
144=9{2a+40}
144=18a+360
18a=144-360
18a= -216
a = -216/18
a = -12
t(n) =a+(n-1) d
t(10)=-12+(10-1)5
t(10)=-12+(9)5
t(10) = -12+45
t(10)=33
t(10)=33,a=-12
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