- #1
Appleton
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Homework Statement
11) The tangent at P on the ellipse [itex] \frac{x^2}{a^2}+
\frac{y^2}{b^2}=1[/itex] meets the x and y axes at A and B.
Find, in terms of the eccentric angle of P, the ratio of the lengths AP and BP.
12) Repeat Question 11 using the normal at P.
Homework Equations
[itex]bx \cos \theta + ay \sin \theta = ab [/itex]
The Attempt at a Solution
[/B]
I had no significant difficulty with 11, my problem was with 12:
The normal at P is
[itex]y=\frac {a\sin\theta}{b\cos\theta}x-\frac{(a^2-b^2)\sin\theta}{b}
[/itex]
When y = 0
[itex]x=\frac{(a^2-b^2)\cos\theta}{a}
[/itex]
So
[itex]A =\left(\begin{array}{cc}\frac{(a^2-b^2)\cos\theta}{a}&0\end{array}\right)[/itex]
When x = 0
[itex]y=-\frac{(a^2-b^2)\sin\theta}{b}
[/itex]
So
[itex]B =\left(\begin{array}{cc}0&-\frac{(a^2-b^2)\sin\theta}{b}\end{array}\right)[/itex]
[itex]AP^2= (a\cos\theta-\frac{(a^2-b^2)\cos\theta}{
a})^2+
(b\sin\theta)^2
[/itex]
[itex]BP^2= (b\sin\theta+\frac{(a^2-b^2)\sin\theta}{
b})^2 +
(a\cos\theta)^2
[/itex]
[itex]\frac{AP^2}{BP^2}=\frac{b^4(a^2\sin^2\theta+b^2\cos^2\theta)}{
a^4(a^2\sin^2\theta+b^2\cos^2\theta)}
[/itex]
[itex]\frac{AP}{BP}=\frac{b^2}{a^2}
[/itex] = the ratio of the lengths AP to BP
However my textbook says the correct answer is
[itex]\frac{a^2}{b^2}
[/itex]