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2h
comment Proper definition of concyclic?
Provided that you're clear that the same $Z$ and $a$ apply across all $z_k$, then: yes, this is a proper definition.
8h
revised Integrating $\int{\frac{x^2}{1+x^5}dx}$
Better title
15h
revised Make $20$ using two “$3$”s
Better title, edited for clarity, removed irrelevant tag
2d
comment What is happening in the picture
The points moving along the diameters are the feet of perpendiculars to those diameters from a point moving along the circumference.
Jun
27
comment What is happening in the picture
The origin of this appears to be a blog post about the "Van Schooten Ellipse", which has some discussion and links to other ellipse-drawing mechanisms.
Jun
26
answered If $\arctan(x)+\arctan(y)+\arctan(z)=\pi/2$ how to show that $xy+yz+zx=1$?
Jun
26
revised Help to solve this geometry problem
Added missing "2"s in final result.
Jun
25
comment Conversion between trig functions and hyperbolic trig functions
See the Gudermannian function.
Jun
25
answered Help to solve this geometry problem
Jun
25
revised Name of the segment connecting a point's coordinate axis projections?
Better title, additional tags
Jun
24
answered Two different trigonometric identities giving two different solutions
Jun
24
awarded  Guru
Jun
24
revised Proving $1+\cot^2(-\theta)=\csc^2(\theta)$
Better title
Jun
23
comment Proof regarding hyperbolas
@Arthur: Form is definitely important to the formula. :) But, if you have $y=mx+c$, then you can re-write it as $mx-y+c=0$, so that $A=m$, $B=-1$, $C=c$. (You could also re-write it as $-mx+y-c=0$, so that $A=-m$, $B=1$, $C=-c$, but the various squares and absolute values in the formula cause the two approaches to give the same result ... as they should.) In particular, the Standard Form equation for directrix $L$ is $1x + 0 y -\frac{ a^2}{c}=0$, so ...
Jun
23
comment Proof regarding hyperbolas
@Arthur: If $P=(p,q)$ and $L: A x + B y + C = 0$, then $$d(P,L) = \frac{|Ap+Bq+C|}{\sqrt{A^2+B^2}}$$
Jun
23
comment Proof regarding hyperbolas
@Arthur: Are you familiar with the formula for the distance between two points and the formula for the distance between a point and a line? If so, use them to re-write the condition $\frac{d(P,F)}{d(P,L)} = e$ in terms of $x$ and $y$ and $a$ and $c$. See where that gets you.
Jun
23
comment Resultant of two polynomials in two variables
Interestingly, for $n=1, 2, 3, \dots, 10$, the coefficient of the leading term is $\left( n(n+1) \right)^{n-1}$.
Jun
23
comment Resultant of two polynomials in two variables
A few test cases in Mathematica suggest that, if $m$ is the parameter in $f$, and $n$ the parameter in $g$, then the degree of $y$ in the resultant is $mn$. This is perhaps not surprising, but it may still be worth mentioning.
Jun
23
comment Equal sign or approximation sign?
If using the equals sign, I'd expect to see $$\theta = 0.3747\dots$$
Jun
23
answered BMO1 2004/05 Question 2 Geometry Problem