Q3 of 105 Page 146

In an AP :

given l = 28, sn = 144 and there are 9 terms Find and a

Given

Last term (l) = 28


Sum of the series sn = 144


The number of terms in the series (n) = 9


We have another formula to find sum of the series, when common difference is not given


Sum of the series sn = [a +l]


Where a is the first term


144 = [a + 28]


32 = a + 28


4 = a


∴ first term (a) = 4.


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