|z1| = {[x + 5^(1/2)]^2 + y^2}^(1/2),
|z2| = {[x - 5^(1/2)]^2 + y^2}^(1/2).
6 = |z1| + |z2|
說(shuō)明點(diǎn)（x,y）到點(diǎn)（-5^(1/2),0）和點(diǎn)（5^(1/2),0）的距離之和為常數(shù)6.
點(diǎn)（x,y）在1個(gè)橢圓上.橢圓的2個(gè)焦點(diǎn)分別為點(diǎn)（-5^(1/2),0）和點(diǎn)（5^(1/2),0）.橢圓的半焦距c = 5^(1/2).橢圓的長(zhǎng)軸在x軸上.
設(shè)橢圓方程為 x^2/a^2 + y^2/b^2 = 1,
則,
3^2 = c^2 + b^2 = 5 + b^2, b = 2.
a^2 = c^2 + b^2 = 5 + 4 = 9,
a = 3.
橢圓方程為 x^2/3^2 + y^2/2^2 = 1,
可設(shè)橢圓上的點(diǎn)（x,y）滿足x = 3cost, y = 2sint. 0