等差（比）数列a1+a2+a3=7 a1a2a3=8 (q＞1).（1）求an通项公式.（2）a7+a8+a9=多少a1a2a3=8(a2)^3=8a2=2a1+a2+a3=7a1+2+a3=7a1+a3=5a2/q+a2q=52/q+2q=52q^2-5q+2=0(2q-1)(q-2)=0q=2或q=1/2(舍去,q＞1）a2=a1q2=2a1a1...