The standard equation of an ellipse with major axis in the x direction is [MATH]\frac{x^2}{a^2}+ \frac{y^2}{b^2}=1[/MATH]. The focal distance equation is [MATH]c^2 = a^2-b^2[/MATH]. The gradient of the left side of the equation of the ellipse is [MATH]\vec N =\langle \frac{2x}{a^2},\frac{2y}{b^2}\rangle[/MATH] and is perpendicular to the ellipse at [MATH](x,y)[/MATH]. Now, if you know [MATH]\vec N[/MATH], you can find the angle you need. Looking at what you are given and what you need, what are your thoughts?