1.（x-1)/2=2/1,
x-1=4,
x=5.
2.a4=a2q^2,q^2=1/4,q>0,
∴q=1/2.an=a2q^(n-2)=2*(1/2)^(n-2)=2^(3-n).
bn=3-n,
Tn=n(5-n)/2.
3.sin(A-π/6)=sin(π/2-A),
在△ABC中,A-π/6∈（-π/6,5π/6）,π/2-A∈（-π/2,π/2）,
∴A-π/6=π/2-A,A=π/3.
B+C=2π/3.
由正弦定理,b+c=a/sinA*(sinB+sinC)=8sin[(B+C)/2]cos[(B-C)/2],
最大值=4√3.