Let the common ratio be q, then q>0
A 1, (1/2)a3 and 2a2 are equal, then
2( 1/2)a3=a 1+2a2
a3=a 1+2a2
a 1q？ =a 1+2a 1q
q？ -2q- 1=0
(q+ 1)(q-2)=0
q =- 1(& lt； 0 or q=2.
(a 20 13+a 20 14)/a 20 1 1+a 20 12)
=(a20 1 1×q？ +a20 12×q？ )/(a 20 1 1+a 20 12)
=q？ (a 20 1 1+a 20 12)/(a 20 1 1+a 20 12)
=q？
=2?
=4