Which term of an A.P. 16, 11, 6, 1,... is -54 ?

Which term of an A.P. 16, 11, 6, 1,... is -54 ?
Solution :
Let -54 be the nth term  of the sequence
tn  = -54
a + (n - 1)d  = -54
a  = 16 , d = 11 - 16  ==> -5
16 + (n - 1)(-5)  = -54
(n - 1)(-5)  = -54 - 16
 (n - 1)(-5)  = -70
 n - 1  = -70/(-5)  ==> 14
n  = 14 + 1 
n  = 15

Hence 15th term of the given sequence is -54.

கருத்துகள் இல்லை: