If 7th times the 7th term of an A.P is equal to 11 times it's 11th term, then find its 18th term.
Answers
7(a+6d) = 11(a+10d)
7a+42d = 11a+110d
- 4a = 68d
a = 68d/ -4 = -17 d eq.1
so 18 th term is
a +17d
ie : putting a value from eq.1
- 17d +17d = 0
therefore the 18th term is 0
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given :-
7 ( a7 ) = 11 ( a11 )
7 ( a + 6d ) = 11 ( a + 10d )
7a + 42d = 11a + 110d
7a - 11a + 42d - 110d = 0
4a - 68d = 0
a - 17d = 0
a = 17d ... ( i )
To find 18th term
a18 = a + ( n - 1 )d
a18 = a + 17d
a18 = 17d + 17d
a18 = 34d
given :-
7 ( a7 ) = 11 ( a11 )
7 ( a + 6d ) = 11 ( a + 10d )
7a + 42d = 11a + 110d
7a - 11a + 42d - 110d = 0
4a - 68d = 0
a - 17d = 0
a = 17d ... ( i )
To find 18th term
a18 = a + ( n - 1 )d
a18 = a + 17d
a18 = 17d + 17d
a18 = 34d
given :-
7 ( a7 ) = 11 ( a11 )
7 ( a + 6d ) = 11 ( a + 10d )
7a + 42d = 11a + 110d
7a - 11a + 42d - 110d = 0
4a - 68d = 0
a - 17d = 0
a = 17d ... ( i )
To find 18th term
a18 = a + ( n - 1 )d
a18 = a + 17d
a18 = 17d + 17d
a18 = 34d