In an A.P 7th term is 23 and 29th term is 85. Find the 18th term in the A.P
?​

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1. Answer:

   In AP

   Given :

   • a7 = 23
   • a9 = 85

   Solution :

   • a + 6d = 23 ~ equation 1
   • a + 8d = 85 ~ equation 2

   Solving equation 1 and 2

   • (-2d) = (-62)
   • 2d = 62
   • d = 62/2
   • d = 31
   • a + 6d = 23
   • a + 6(31) = 23
   • a + 186 = 23
   • a = 23 – 186
   • a = (-163)

   a18 = a + 17d

   • a18 = (-163) + 17(31)
   • a18 = (-163) + 527
   • a18 = 364

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