# Find the equation of the set of points $P$ the sum of whose distance from $(4,0,0)$ and $(-4,0,0)$ is equal to $10$
$\begin{array}{1 1}16x^2+25y^2+25z^2+225=0 \\9x^2+25y^2+25z^2-225=0 \\ 9x^2+25y^2+25z^2+225=0 \\16x^2+25y^2+25z^2-225=0 \end{array}$