Question

(vi) given a = 2, d=8, S = 90, find n and an
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Answer 1

Answer:

n = 5 and an = 34

Explanation:

Sum = n [2a + (n-1) d]

            2

==: 90 = n [2*2 + (n-1) 8]

              2

==: 90 * 2 = n [4 + 8n - 8]

==: 180 = 8n² - 4n

==: 8n² - 4n - 180 = 0

==: 2n² - n - 45 = 0

==: n = 5

an = a + (n - 1) d

an = 2 + (5 - 1) 8

an = 2 + 32

an = 34

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