5th trm is 1/3
9th trm is 16/243
a×r raise to the power 4/ a×r raise to the power 8= 81/3×16
= 1/ r raise to the power 4 = 81/16
Or r raise to the power 4 = 16/81
= r= + & - 2/3
And substitute the value of a nd r in formula a×r raise to the power 3 in order to find 4th term.
