应该是公差不为零的等差数列｛a n｝,设公差为D因为A(3)=A(1)+2DA(4)=A(1)+3DA(7)=A(1)+6Da4是a3与a7的等比中项则(A(1)+2D)(A(1)+6D)=(A(1)+3D)^2A(1)^2+8D*A(1)+12D^2=A(1)^2+6D*A(1)+9D^2 2D*A(1)+3D^2=0...