Find the sum of the series 21+15+9+...to 20 terms
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Answered by
11
a=21
d=15-21=>-6
n=20
Sn=n/2(2a+(n-1)d)
=>10(42+19*-6)
=>10(42-114)
=>10*-72
=>-720
d=15-21=>-6
n=20
Sn=n/2(2a+(n-1)d)
=>10(42+19*-6)
=>10(42-114)
=>10*-72
=>-720
aryadas:
understand???
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Answered by
1
-720 is the answer of this question
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