Use implicit differentiation to find the slope of the tangent line of each graph at point (x,y). The slope is, of course, the tangent of the angle each makes with the x-axis. And the angle between the tangent lines (which is, by definition, the angle between the curves) is the difference between those two angles. Use the trig indentity .
You will need to know, if you do not already, that the eccentricity of the ellipse, , is given by (for a> b) and that the eccentricity of the hyperbola, , is given by (also for a> b).