Question

Find the 17th term from the end of the AP:1,6,11,16,_ _ _ _211,216(solution)

Answer 1

Hi ,

Given A. P is 1 , 6 , 11 , 16 , ......, 211 , 216

Rearrange the A .P in reverse order

216 , 211 , ....... , 16 , 11 , 6 , 1

First term = a = 216

Common difference = d = a 2 - a 1 = 211 - 216 = - 5

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If a and d are first term and common difference in an A . P

n th term = a n = a + ( n - 1 ) d

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Now ,
a = 216

d = -5,

n = 17

17 th term = a 17

a 17 = a + 16 d

= 216 + 16 ( -5 )

= 216 - 80

= 136

Therefore ,

Required 17 th term = 136.

I hope this will usful to you.

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Answer 2

Given,

a=216 ( by reversing )

d=a2-a1=211-216= -5

a17= a+16d

a17=216+16*-5

a17=216-80

a17=136