find the sum of the series 51+50+49+......+21
Answers
Answered by
16
Step-by-step explanation:
51 + 50 + 49 +..... + 21
a = 51, d = -1, an = 21
∴ a + (n-1) d = an
51 + (n-1)(-1) = 21
(n-1)(-1) = 21 - 51
n-1 = 30
∴ n = 31
∴ Sum of the series = 31/2(51+21)
= 31/2 × 72
= 1116
please mark my answer as brilliant.
Answered by
1
Answer:
an=a+(n-1)d. (d=50-51=-1)
21=51+(n-1)(-1)
21-51=-n+1
-31=-n+1
n=1+31
n=32
Sum of AP =n/2{a+an}
=32/2(51+21)
=16(72)
=1152
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