The nth term of a geometric sequence = ar^(n – 1)
2nd term =4=ar^(2-1)=ar
ar=4 .........eq1
6th term=16=ar^(6-1)=ar^5
ar^5=16 ........eq2
eq2/eq1 gives
ar^5/ar=16/4
r^4=4
(r^2)^2=2^2
r^2=2
r=sqrt2
substituting in eq1 we get
a(sqrt2)=4
a=4/(sqrt2)=2sqrt2
4th term=ar^3=2sqrt2(sqrt2)^3=2(sqrt2)^4=2(4)=8