find the sum of the first 20 terms of series 1+2+3+......
Answers
Answered by
5
Answer:
- n/2(last term + first term)
Step-by-step explanation:
- 20/2(20+1)
- 10×21=210
Answered by
2
Answer:
here
a = 1
d = a2-a1 = 2-1 = 1
an = 20
an = a + ( n-1 ) × d
20= 1 + ( n - 1 ) × 1
20= 1+ 1n - 1
20= 1n
n = 20
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