Find the 19th term of an A.P. -11,-15,-19,...

Find the 19th term of an A.P. -11,-15,-19,...
Solution :
nth term of the A.P
tn  = a + (n - 1)d
a = -11 , d = -15 - (-11)  = -15 + 11 ==> -4
t19  = -11 + (19 - 1)(-4)
=  -11 + 18(-4)
=  - 11 - 72
t19  =   -83

Therefore, the 19th term of the A.P. is -83. 

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