Question 628200
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Hi,
 Standard Form of an Equation of an Ellipse is {{{(x-h)^2/a^2 + (y-k)^2/b^2 = 1 }}} 
where Pt(h,k) is the center. (a variable positioned to correspond with major axis)
 a and b  are the respective vertices distances from center
 and ±{{{sqrt(a^2-b^2)}}}are the foci distances from center: a > b
{{{x^2/49-y^2/64=1}}}   C(0,0) and {{{f[d] = sqrt(64-49) = sqrt(15)}}}
 foci are (0, ±{{{sqrt(15)}}})