How to show the angle is $\frac{\pi}{2}$ which between tangent of an ellipse and its chord that through the focus?
39906
Equation of the locus of the foot of perpendicular from any focus upon any tangent to the ellipse ${x^2\over a^2}+{y^2\over b^2}=1$
122169
Prove $\sin(\pi/2)=1$ using Taylor series
119815
Why is $\tan((1/2)\pi)$ undefined?
155868
How can I find the difference between two angles?
23397
Why it's true? $\arcsin(x) +\arccos(x) = \frac{\pi}{2}$
72157
Elementary proof of tangent half angle formula
125171
Help with this trigonometry problem?
36701
$\displaystyle\int_{0}^{2\pi}\frac{1}{a+ \cos\theta}\,d\theta$
158210
showing $\arctan(\frac{2}{3}) = \frac{1}{2} \arctan(\frac{12}{5})$
116815
Angle between two circles
120953
Show that, $2\arctan\left(\frac{1}{3}\right)+2\arcsin\left(\frac{1}{5\sqrt2}\right)-\arctan\left(\frac{1}{7}\right)=\frac{\pi}{4}$
120379
The Path of the center of a cutting tool that will cut out an ellipse (x/4)2+(y/2)2=1
127284
Closed form of $\int_0^{\pi/2} \frac{\arctan^2 (\sin^2 \theta)}{\sin^2 \theta}\,d\theta$
17769
Show that $\frac{\sin x}{\cos 3x}+\frac{\sin 3x}{\cos 9x}+\frac{\sin 9x}{\cos 27x} = \frac{1}{2}\left(\tan 27x-\tan x\right)$
105280
How to find the equation of a parabola given the tangent equations to two points?
13534
How to plot an ellipse?
9539
$\alpha$ and $\beta$ are solution of $a \cdot \tan\theta + b \cdot \sec\theta = c$ show $ \tan(\alpha + \beta) = \frac{2ac}{a^2 - c^2}$