数列{an}的前n项和为Sn,若a1="1," an+1 =3Sn(n ≥ 1),则a5=
以抛物线的焦点为圆心,且过坐标原点的圆的方程为___________
已知直线与圆相切,则的值为___________
=___________
直线的倾斜角为,则的值是___________
计算行列式=____________