a4=a1q^34=1/2q^3q^3=8q=2a1a2+a2a3+……+ana(n+1)=a1*a1q+a1q*a1q^2+.+a1q^(n-1)*a1q^n=(a1)^2*[1*q+q*q^2+q^2*q^3+.+q^(n-1)q^n]=(a1)^2*[q+q^3+q^5+.+q^(2n-1)]=(a1)^2*{q*[1-(q^2)^n]/(1-q^2)}=(a1)^2*{q*[1-q^2...