Find the sum of first 16 terms of an Arithmetic Progression whose
4th and 9th terms are
–
– .​

1 thought on “Find the sum of first 16 terms of an Arithmetic Progression whose<br />4th and 9th terms are<br />–<br />– .​”

1. Answer:

   4th term = a + 3d = 15

   9th term = a + 8d = -30

   – – +

   ————————

   -5d = 45

   d = -9

   so, a = 15-3(-9) = 15+27 = 42

   so, A16 = a+(n-1)d = 42 + (16-1)(-9)

   = 42-135

   = -93

   so, S16 = 8(42-93)

   = 8(-51)

   = -408 … ans

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