x^2/a^2+y^2/b^2=1
焦点F1(-c,0), F2(c,0)
顶点A1(-a,0)A2(a,0)
双曲线
焦点F1’(-a,0) F2'(a,0)
顶点A1'(-c,0) A2'(c,0)
x^2/c^2-y^2/b^2=1
x^2/c^2-y^2/b^2=0
y^2=b^2x^2/c^2
y=bx/c y=-bx/c
x^2/a^2+(b^2x^2/c^2)/b^2=1
x^2/a^2+x^2/c^2=1
x^2=a^2c^2/(a^2+c^2)
y^2=a^2b^2/(a^2+c^2)
x^2=y^2,b^2=c^2
a^2=b^2+c^2=2c^2
1/2=c^2/a^2=e^2
e=√2/2