(1)c^2=1设椭圆方程为x^2/a^2+y^2/(a^2-1)=1把C点坐标代入,解得a^2=4椭圆方程为x^2/4+y^2/3=1(2)P（2cosθ,3^0.5sinθ）则→PF1*→PF2=t=4cosθ^2-1+3sinθ^2→PF1*→PF2=t=2+cosθ^2∵cosθ^2∈[0,1]∴t∈[2,3]...