Find the sum of first 20 terms of the A.P. 1, 4, 7, 10, ..... .
Answers
Answered by
5
Answer:
S20=590
Step-by-step explanation:
A.P. 1, 4, 7, 10, .....
a=1, d=4-1=3, n=20
Sn=n/2[2a+(n-1)d]
S20=20/2[2(1)+(20-1)3]
S20=10(2+(19)3]
S20=10(2+57)
S20=10(59)
S20=590
Therefore, the sum of first 20 terms is 590.
Answered by
3
Answer:
590
Step-by-step explanation:
By arthemetic progression formulas,
Sum of n terms = n/2 (2a + (n-1) d)
a, first term = 1
d, common difference = 3
n = 20
Therefore, Sn = 20/2 (2(1) + (20-1) 3)
= 10 (2 + 19*3)
= 10 (2 + 57)
= 10 (59)
= 590
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