if the sum of first 18 term of an ap is 639 and its first term is 10 find the 25th term
Answers
Answered by
2
Step-by-step explanation:
sum = 639
n = 18
a = 10
Sn = n/2 [2a + (n - 1)d]
639 = 18/2 [2(10) + (18 - 1)d]
639 = 9[20 + 17d]
639/9 = 20 + 17d
71 = 20 + 17d
71 - 20 = 17d
51 = 17d
51/17 = d
d = 3
an = a + (n - 1)d
an = 10 + 24(3)
an = 10 + 72
an = 82
hope this will help you
mark me brainliest
follow me..
Similar questions