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i)given a-2, d=8,s-90, find n anda. |
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Answer» Sn = (n/2)(2a+(n-1)d)90 = (n/2)(4+(n-1)8)180 = n(8n-4)180 = 8n^2-4n8n^2-4n-180 = 0n=5 an = a + d (n -1 )Sn = n * [ a + a + d (n-1) ] / 2 = n * mean of 1st term and nth term90 = n * [ 4 + 8 n - 8 ] /2 => 180 = 8 n² - 4 n => 2 n² - n - 45 = 0n = 5 => an = 2 + 4 * 8 = 34 tq This is correct answers |
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