Reputation
1,722
Top tag
Next privilege 2,000 Rep.
Edit questions and answers
Badges
8 28
Impact
~62k people reached

Nov
27
comment Is the empty set the only possible set for $A$ such that $A=\{x|x\not\in A\}$?
The most understandable answer. :-) Thanks.
Aug
9
comment How to test whether a set of four points can form a parallelogram
We can save the calculation just by calculating the midpoint times 2 to avoid dividing by 2.
Aug
9
comment How to test whether a set of four points can form a parallelogram
How about the case there are 3 points on a line?
Aug
9
comment How to test whether a set of four points can form a parallelogram
But all of your three tests may be false even though the given 4 points can be vertices of a parallelogram.
Aug
9
comment How to test whether a set of four points can form a parallelogram
If $P_1$ is the opposite of $P_3$ then the last two tests are false. So the first test might be either false or true.
Aug
9
comment How to test whether a set of four points can form a parallelogram
I think we need 4 tests. Your answer needs one more test which is $\vec{P_1P_2}=\vec{P_3P_4}$.
Aug
9
comment How to test whether a set of four points can form a parallelogram
Please explain why you compared just those vectors.
Aug
9
comment How to test whether a set of four points can form a parallelogram
@augurar: The given points are randomly chosen from a set of some points. The order is not known.
Jul
4
comment Is my theorem correct? $f(x) \leq g(x)$ for $x\geq a$ iff $f'(x) \leq g'(x)$ for $x\geq a$ and $f(a)=g(a)$.
what is the name of the well known corollary?
Jul
4
comment Is my theorem correct? $f(x) \leq g(x)$ for $x\geq a$ iff $f'(x) \leq g'(x)$ for $x\geq a$ and $f(a)=g(a)$.
By assuming the right side is satisfied first and prove that the left is either correct or incorrect.
Jul
4
comment Is my theorem correct? $f(x) \leq g(x)$ for $x\geq a$ iff $f'(x) \leq g'(x)$ for $x\geq a$ and $f(a)=g(a)$.
Could you prove in both directions?
May
7
comment What is the non-piecewise curve that resembles the following roller coaster track?
@Neil: Any parameter is accepted.
May
7
comment What is the non-piecewise curve that resembles the following roller coaster track?
@vonbrand: I don't want to use if-then-else construct in my code. :-)
May
7
comment What is the non-piecewise curve that resembles the following roller coaster track?
I cannot show my effort to solve this problem. Is it necessary to show it?
May
7
comment Functions Question
Commutative by accident.
Mar
11
comment How to prove that we cannot see more than 3 faces of an opaque solid cube simultaneously?
+1. Makes sense!
Mar
11
comment How to prove that we cannot see more than 3 faces of an opaque solid cube simultaneously?
But you can see 3 faces by focusing on one corner.
Feb
10
comment How to prove the number of images of two mirrors inclined at $A$ is $360/A -1$
+1 Short respons: I ask myself to prove it analytically. :-) I will give other comments later as I am teaching right now. :-) thanks.
Jan
21
comment How to find the closed solution for the following recursive vector equations?
OK. I am waiting for other solutions if any.
Jan
21
comment How to find the closed solution for the following recursive vector equations?
@heropup's solution in his comment seems to be much more better.