請移動點 K , 觀察點 P 的軌跡

=\overline{ PK }+\overline{ PB }+\overline{ DA }=\overline{ KB }+\overline{ DA }

因為 \overline{ PA }+ \overline{ PB }= \overline{ PD }+\overline{ DA }+ \overline{ PB }

=半徑7+半徑1=定值8

所以 P 點的軌跡為一橢圓 ,
此橢圓兩焦點為A、B ,
長軸長為8

圓B:(x-2)²+y²=49

圓A:(x+2)²+y²=1

A = Point(xAxis)
K = Point(d)
B = (2, 0)
a = Segment(B, K)
b = Segment(A, K)
C = Intersect(e, d)
P = Intersect(e, a, 1)
f = Circle(P, K)
D = Intersect(c, f, 1)
g = Segment(A, P)