Answer the following
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Answer:
n = 8
Step-by-step explanation:
Given data:
Sn = 180, a1 = 5, d = 5, n = ?
Sn = n/2 [ 2a + (n - 1) d ]
180 = n/2 [ 2×5 + (n - 1)5 ]
180 = n/2 [ 10 + 5n - 5 ]
180×2 = n [ 5 + 5n ]
360 = 5n [ 1 + n ]
360/5 = n + n^2
n^2 + n -72 = 0
n^2 + 9n - 8n - 72 = 0
n (n + 9) - 8 (n + 9) = 0
(n - 8) = 0 or (n + 9) = 0
n - 8 = 0 n + 9 = 0
n = 8 or n = -9
n will not be in negative so answer is 8
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