how many terms of A.P 30,48,66 must be taken to get the sum 4020
Answers
Answered by
1
Step-by-step explanation:
a = 30
d = 48 - 30
d =18
Sn = 4020
Sn = n/2(2a + (n-1)d)
4020 = n/2 (60 + (n-1)18)
8040 = 60n +18n^2 - 18n
42n + 18n^2 - 8040 = 0
9n^2 + 21n - 4020 = 0
3(3n^2 +7n-1340) = 0
3n^2 +67n -60n -1340 = 0
(3n - 60) (3n + 67)
n = 20 / - 67/3
since the terms can't be negative so
n = 20
Similar questions