Question -
Answer -
In A.P 9, 7, 5, тАжтАжтАж
Here first term (a) = 9 and d = 7 тАУ 9 = -2 {or 5 тАУ 7 = -2}
nth term (an) = a + (n тАУ 1) d = 9 + (n тАУ 1) (-2) = 9 тАУ 2n + 2 = 11 тАУ2n
Now in A.P. 15, 12, 9, тАж..
Here first term (a) = 15 and (d) = 12 тАУ 15 = -3
nth term (an) = a + (n тАУ 1) d = 15 + (n тАУ 1) x (-3)
The nth term of first A.P. = nth term of second A.P.
11 тАУ 2n = 18 тАУ 3n
=> -2n + 3n = 18 тАУ 11
=> n = 7
Hence n = 7