Arithmetic Sequence

Question

Find the 21st term of the arithmetic sequence 

Answer 1

Given AP -2/8, -1/16, 1/8, 5/16...........

t1  =  a  =  -2/8

t2  =  -1/16

d  =  t2 - t1

    =  -1/16  -  (-2/8)

    =  -1/16  + 2/8

    =  (-1 + 4) / 16

d  =  3 / 16

nth term tn = a + (n-1)d --------------> (1)

Substitute a  =  -2/8 and d  =  3/16 and n = 21 in Eq (1)

t21  =  -2/8 + (21 - 1)(3/16)

       =  -2/8 + (20)(3/16)

       =  -2/8 + 30/8

       =  (-2 + 30 ) / 8

       =  28/8

       =  7/2.

Amswer :

The 21st term is 7/2.