how many terms of AP -10,-7,-4,-1,,,,must be added to get the sum 104?
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Answer:
sum of AP = n/2 ( 2a + (n-1)d)
difference d = -7 - (-10) = 3
a = first term = -10
104 = n/2 ( -20 + 3n - 3 )
208 = n( 3n - 23 )
3n² - 23n - 208 = 0
on solving n = 13
therefore 13 terms
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