Question

In a GP the sum of 2nd and 4th term is 30.The difference of 6th and 2nd term is 90.Find the 8th term of GP whose common ratio is greater than 1.

Answer 1

* 2nd and 4th term=30.
=a+d+a+3d=30
=2a+4d=30
=a+2d=15 ( 1 )

* difference of 6th and 2nd term =90
=a+5d - a+d =90
=6d= 90
=d= 90/6
=d= 15

d = 15 ( 1 )
=a+2d =15
=a+2×15 =15
=a+30 =15
=a= 15 - 30
=a = -15

* 8term is
= a+7d
= -15+7×15
= -15+105
= 90

* 8term is 90. ✓

Answer 2

the answer of 8th term is 90