Question 419385
  <pre><font face = "Tohoma" size = 4 color = "indigo"><b>
Hi
18x^2+36y^2=648
 18x^2/648 + 36y^2/648 = 1
   x^2/36 + y^2/18 = 1
 sqrt(36-18) = sqrt(18) = 3sqrt(2)
foci are (3sqrt(2),0) and (-3sqrt(2),0)
{{{drawing(300,300,   -10,10,-10,10,  arc(0,0,12 ,8.5),
 grid(1),
circle(4.24, 0,0.4),
circle(-4.24, 0,0.4),
graph( 300, 300, -10,10,-10,10))}}}