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kennytm
  • Member for 13 years, 9 months
  • Last seen more than 1 year ago
92 votes

Why does $\tan^{-1}(1)+\tan^{-1}(2)+\tan^{-1}(3)=\pi$?

55 votes

Why are $3D$ transformation matrices $4 \times 4$ instead of $3 \times 3$?

48 votes
Accepted

Why is $\int\limits_0^1 (1-x^7)^{1/5} - (1-x^5)^{1/7} dx=0$?

29 votes
Accepted

Can this gravitational field differential equation be solved, or does it not show what I intended?

27 votes
Accepted

How is prisoner's dilemma different from chicken?

21 votes
Accepted

About powers of irrational numbers

20 votes
Accepted

Why is this matrix neither positive nor negative semi-definite?

19 votes
Accepted

Algorithm for calculating $A^n$ with as few multiplications as possible

19 votes
Accepted

Looking for functions $f$ with $\int_{-\infty}^{\infty}f(x)\,dx = 1$.

17 votes
Accepted

What is the optimum angle of projection when throwing a stone off a cliff?

10 votes
Accepted

Uniqueness of $\sin x$ and $\cos x$? (Putnam Exam problem)

9 votes
Accepted

Infinite series: $1/2 + 1/(1\cdot 2 \cdot 3) + 1/(3\cdot 4 \cdot 5) + \ldots$

8 votes
Accepted

Indefinite summation of polynomials

8 votes

Smallest number of points on plane that guarantees existence of a small angle

7 votes
Accepted

Gorgeous diophantine equation

7 votes
Accepted

Simple 2 equations and 2 unknowns

7 votes
Accepted

Function behavior with very large variables

7 votes
Accepted

Why does the log-log scale on my Slide Rule work?

7 votes
Accepted

How do you take the derivative of a variable with respect to a different variable:

7 votes

Multiples of 4 as sum or difference of 2 squares

6 votes

Proof about an infinite sum: $\sum_{k=1}^\infty \frac1{k^2+3k+1} \ge \frac12$

6 votes

problem with inequality

6 votes

Is $a \sin x + b \sin y \leq \sin(ax + by)$ true?

6 votes

Show that $A∩B∩C= ∅$ is only true when $A∩B = ∅, A∩C = ∅$ or $B∩C = ∅$ or show a counterexample.

6 votes
Accepted

About prefactor in book's Gamma function identity

5 votes
Accepted

Solve $y'(t)=t+1$ using Laplace transform

5 votes
Accepted

logic operations on proposals

5 votes
Accepted

Proving identity $\sum_{j\geq 1}[(j+t)^{-1}-j^{-1}]=\sum_{k\geq 1}\zeta (k+1)(-t)^{k}$

4 votes
Accepted

Einstein notation - difference between vectors and scalars

4 votes

Which one is bigger $2^{n!}$ or $(2^{n})!$?