Question

If 7 times the 7th term of an AP is equal to 11 times its 11th term,then find its 18th term

Answer 1

7(a7) = 11(a11)

=> 7 (a + 6d) = 11 ( a + 10d)

=> 7a + 42d = 11a +110d

=> -4a = 68d

=> a = -17d

=> -a = 17d -----------(1)

a18 = a + 17d ( from 1)

=> a18 = a + (-a)

=> a18 = 0

Answer 2

7( a+6d)=11(a+10d)
7a+42d=11a+110d
4a+ 68d=0
a+17d=0
a18 =0

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