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Jul
27
answered The set of all real functions of a real variable
Jul
22
revised If I buy 2 lottery tickets do I double my chance of winning?
Removed unattributed claims about "Mathematicians" and what "The Internet" says. The entire paragraph didn't add anything to the question.
Jul
22
comment Odds of winning the lottery if I buy 10,000,000 tickets
blogs.scientificamerican.com/guest-blog/… a texas jackpot hit 1.3$ rate-of-return. nytimes.com/1992/02/25/us/… is someone actually doing it. Punchline? Investment theory says even positive ROI tickets are not good investments! maa.org/programs/maa-awards/writing-awards/…
Jul
22
suggested approved edit on If I buy 2 lottery tickets do I double my chance of winning?
Jul
22
comment Why do we show that structures aren't isomorphic by exhibiting a property not shared by one of them?
@MartinBrandenburg "I don't completely agree" doesn't seem to add any useful information: Can you explain what you disagree with, and why, instead of just stating there is something you disagree with? Is this approach not common in different areas of math? Is that phrase not often omitted from proofs?
Jun
12
answered What are “instantaneous” rates of change, really?
Jun
12
comment What are “instantaneous” rates of change, really?
This answer seems to neglect the fact you can use infinitesimals to build a rigorous definition of calculus.
May
26
answered Understanding derivatives
May
14
awarded  Yearling
May
11
answered Why is $1/i$ equal to $-i$?
May
7
answered Is there an intuitive, not-too-mathematical way of thinking about limit points?
May
5
comment Universal quadratic formula?
@Mehrdad Then if b and c is zero, the above returns an indeterminate value for x2 -- 0/0. If b and a are zero, then the above returns an indeterminate value for x1 (again 0/0). Even in the extended reals, those don't work.
May
5
comment Universal quadratic formula?
This finds solutions in the extended real number line. What does sgn return if b is zero?
May
4
awarded  Critic
Apr
13
answered Limit of f(x) knowing limit of f(x)/x
Mar
17
comment Does the square or the circle have the greater perimeter? A surprisingly hard problem for high schoolers
I might expect a high school student to prove division by $(r+a)$ is valid (neither are $\leq 0$). And $perimeter of square = 32/5 r = 6.4 r$ explicitly might make people happy. The ratio math to show that $6.4 > 2 \pi$ while cute might even be omitted at that point.
Mar
16
comment Does the square or the circle have the greater perimeter? A surprisingly hard problem for high schoolers
If you set radius to r, half the side length to b, and a such that a+r=2b (distance from center of circle, to closest midpoint of square), then solve for a in terms of r and simplify fractions along the way, the 3,4,5 triangle falls out. No coordinate system needed, not assumption that something is unit distance.
Jan
13
comment Is there a law that you can add or multiply to both sides of an equation?
@DanChristensen or the observation that $f(x) = x+b$ is injective
Jan
7
awarded  Autobiographer
Dec
15
answered Can a matrix have the same range and nullspace?