AP: 13,8 3,.............
Find the
sum
of the first 20 tearns.
Answers
Answered by
0
Answer:
-690
Step-by-step explanation:
Answered by
2
Answer:
a = 13 , d = 8 - 13 = -5
sum of n terms = n/2 ( 2a + ( n-1) d )
sum of 20 terms = 20 /2 (2×13 + (20 - 1) (-5) )
= 20/2 ( -69 )
= 10 × (-69 )
= -690
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