设这四个数是a,aq,aq^2,aq^3 所以成等差数列得四个数是a-1,aq-1,aq^2-4,aq^3-13 所以aq-1-（a-1）=aq^2-4-(aq-1)=aq^3-13-(aq^2-4) aq-1-（a-1）=aq^2-4-(aq-1) 即aq^2-2aq+a-3=0 a(q-1)^2=3 a=3/(q-1)^2 aq-1-（a-1...