### Ellipse

goals
The ellipse $\dfrac{x^2}{a^2}+\dfrac{y^2}{b^2}=1$ and the straight line $y=mx+c$ intersect in real points only, if?
Given two fixed points $\mathrm{A}$and $\mathrm{B}$ and $\mathrm{A}\mathrm{B}=6$, then the simplest form of the equation to the locus of $\mathrm{P}$ such that $\mathrm{P}\mathrm{A}+\mathrm{P}\mathrm{B}=8$  is: