Thank you for your responce.
I used a=1
b=2
c=3
for coordinates of A(1,2,3) and center(0,0,0)
now my equaation becomes for point p(x,y,z) on ellipsoid
x=0+(1-0)t=t
y=0+(2-0)t=2t
z=0+(3-0)t=3t
put in ellipsoid equation
t^2/1+4t^2/4+9t^2/9=1
3t^2=1
t=sqrt(1/3)=.57
x=.57...