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Answer:
n = 5
Step-by-step explanation:
Given,
First term of AP, a = 2
Common difference, d = 8
Sum of n terms, Sn = 90
Sum of n terms is given by,
Sn = n/2 * [2a + (n - 1)d]
90 = n/2 * [2(2) + (n - 1)(8)]
90 = n/2 * [4 + 8n - 8]
90 = n/2 * [8n - 4]
90 = n/2 * [2(4n - 2)]
90 = n * (4n - 2)
90 = 4n² - 2n
0 = 4n² - 2n - 90
0 = 2n² - n - 45
n = 5, or n = -9/2
nth term cannot be in decimal.
Hence n = 5
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