c^2=a^2-b^2 =1+2=3
PF1+PF2=2a lPF1-PF2l=2 PF1*PF2=3 (PF1>PF2)
(PF1+PF2)^2=(PF1-PF2)^2+4PF1*PF2=4+12=16
PF1+PF2=4=2a
a=2
a^2-b^3=3 b=1
所以x^2/4 +y^2=1
c^2=a^2-b^2 =1+2=3
PF1+PF2=2a lPF1-PF2l=2 PF1*PF2=3 (PF1>PF2)
(PF1+PF2)^2=(PF1-PF2)^2+4PF1*PF2=4+12=16
PF1+PF2=4=2a
a=2
a^2-b^3=3 b=1
所以x^2/4 +y^2=1