依题意a3*a7=(a1+2d)(a1+6d)=-12,①a4+a6=2a1+8d=-4,a1=-4d-2,②把②代入①，得(-2d-2)(2d-2)=-12,-4d^2+4=-12,16=4d^2,d^2=4,d>0,所以d=2.代入②，a1=-10,所以an=-10+2(n-1)=2n-12.
