Q7 of 89 Page 51

The sum of the 5th and the 7th terms of an AP is 52 and the 10th term is 46. Find the AP.

Let the first term, common difference be a and d respectively.


As we know


an = a + (n - 1)d


and Given


a5 + a7 = 52


a + 4d + a + 6d = 52


2a + 10d = 52


a + 5d = 26


a = 26 - 5d [ eqn i]


also we have given


a10 = 46


a + 9d = 46


26 - 5d + 9d = 46 [ from eqn i]


4d = 46 - 26


4d = 20


d = 5


using this value in eqn I , we get


a = 26 - 5d


a = 26 - 5(5)


a = 1


as a = 6 and d = 5


So, required AP is a, a + d, a + 2d, a + 3d, …. i.e., 1, 1 + 5, 1 + 2(5), 1 + 3(5), …. i.e., 1, 6, 11, 16, …


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