a2/a 1=a3/a4=2,a3/a 1=2^2=4

(2a 1+a2)/(2 a3+a4)=(2a 1+2a 1)/(2 a3+2 a3)= a 1/a3 = 1/4

2.{an} is a geometric series, and let the common ratio be q.

a 1+a2+a3=7，a 1a2a3=8

a 1( 1+q+q^2)=7,a 1^3*q^3=8

a 1^3=7^3/(q^2+q+ 1)^3=8/q^3

8*(q^2+q+ 1)^3=343*q^3

2*(q^2+q+ 1)=7*q

2q^2-5q+2=0

q^2-5/2q+ 1=0

(q-5/4)^2=9/ 16

Q-5/4=3/4 or -3/4

Q=2 or 1/2

When q=2

a 1+a2+a3=7a 1=7

a 1= 1

{an} is 1 as the first term, and 2 is the common ratio sequence.

Q= 1/2

a 1+a2+a3=7/4a 1=7

a 1=4

{an} is a series with 4 as the first term and 1/2 as the common ratio.

3.a, B and C make geometric series.

A/b=b/c= radical sign (a/c)