Points R 1 and R 2 in Figure 25 are defined so that F 1 R 1

Question:

Points Rand R2 in Figure 25 are defined so that F1R1 and F2R2 are perpendicular to the tangent line.
(a) Show, with A and B as in Exercise 70, that

+ c B = 2-c C 022 B = A B

(b) Use (a) and the distance formula to show that

FR P F2R2 B2

(c) Use (a) and the equation of the tangent line in Exercise 70 to show that

B: B(1 + Ac) A+ B B: B(1 - Ac) A+ B


Data From Exercise 70

We prove that the focal radii at a point on an ellipse make equal angles with the tangent line L. Let P = (x0, y0) be a point on the ellipse in Figure 25 with foci F1 = (−c, 0) and F2 = (c, 0), and eccentricity e = c/a.

L R = (a, B) F = (-c, 0) P = (xo, Yo) 1 01 0 R = (, B) F= (c, 0) x

Show that the equation of the tangent line at P is Ax + By = 1, where A = x0/a2 and B = y0/b2.

We prove that the focal radii at a point on an ellipse make equal angles with the tangent line L. Let P = (x0, y0) be a point on the ellipse in Figure 25 with foci F1 = (−c, 0) and F2 = (c, 0), and eccentricity e = c/a.

L R = (, B) F = (-c, 0) P = (xo, Yo) 1 01 0 R = (, B) F= (c, 0) x

Show that the equation of the tangent line at P is Ax + By = 1, where A = x0/a2 and B = y0/b2.

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Calculus

ISBN: 9781319055844

4th Edition

Authors: Jon Rogawski, Colin Adams, Robert Franzosa

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