1.因为lga1 lga2lga4成等差数列故2lga2= lga1+lga4即 a2^2 =a1*a4 又 an 是不同正数的等差数列故a4 = a1+3da2 =a1+d (d>0,a1>0)(a1+d)^2 = a1*(a1+3d)故a1d = d*d 即 a1 = d an = nd bn = 1...