Question

SEQUENCES AND SERIES

Answer 1

Answer:

Step-by-step explanation:

As we Know that formula for arithmetic sequence is

$a_n=a_1+(d-1)$

and for geometric sequence is

$a_n=a1*r^(n-1)$

So,

According to given conditions

     $a+7d=a*r^5 (i)\\ a+19d=a*r^7 (ii)$

By dividing equation (i) and (ii)

Hence proved that

$r^2=a+19d/a+7d$