Noble Mushtak's user avatar
Noble Mushtak's user avatar
Noble Mushtak's user avatar
Noble Mushtak
  • Member for 7 years, 2 months
  • Last seen this week
73 votes
Accepted

Why is $A^TA$ invertible if $A$ has independent columns?

57 votes
Accepted

How to prove that a very large number is not prime

33 votes

Exactly when and why can a Turing-machine not solve the halting problem?

21 votes

Solving an equation, need help with explaining why one solution cant be true

15 votes
Accepted

I don't understand this definition of the integers.

12 votes
Accepted

Negation of "and" statements: a and b

10 votes

Minimize the function $f(y_1,y_2)=3 y_1^2+8y_2^2$

10 votes
Accepted

Proof of $+0 = -0$

9 votes
Accepted

Trying to parse a Putnam solution from 1995

9 votes
Accepted

Analytic continuation of harmonic series

9 votes
Accepted

Series $e^1+e^2+\:...\:+e^n$

8 votes
Accepted

Let $f$ be continuous on $[0,1]$ such that $\int_0^x f = \int_x^1 f$, what is $f$?

8 votes
Accepted

What is the relationship between the orbit-stabilizer theorem and Lagrange's theorem?

8 votes

If irrational numbers are uncountable, then why did I find this?

8 votes

Is there a way to find this limit algebraically? $\lim\limits_{x\to \infty} \frac{x}{\sqrt{x^2 + 1}}$

8 votes
Accepted

The sequence defined by $x_{n}=\frac{x_{n-1}+x_{n-2}}{2}.$

7 votes

What is the sum of the $81$ products in the $9 \times 9$ multiplication grid?

7 votes
Accepted

Any digit written $6k$ times forms a number divisible by $13$

7 votes

If every intermediate ring of a field extension is a field, then the extension is algebraic

7 votes
Accepted

Stuck with this limit of a sum: $\lim _{n \to \infty} \left(\frac{a^{n}-b^{n}}{a^{n}+b^{n}}\right)$.

7 votes

If derivative goes to $0$, does the function have a limit?

7 votes
Accepted

Choosing code using digits and letters

7 votes

How do you create an alternating series with the sign being the same twice in a row?

7 votes
Accepted

Prove this using counting techniques: $\sum_{k=0}^{n}{\binom{2n+1}k} = 2^{2n}$

7 votes
Accepted

Are these two statements true or false?

7 votes

the New Year will be 2017: how many pairs of integer solutions to $x^2 + y^2 = (2017)^3$?

6 votes
Accepted

Confusion about elements in fields, like -1 in Z5

6 votes
Accepted

Solve $(x+1)dx+e^ydy=0$ at (x,y)=(0,1)

6 votes
Accepted

What is the smallest possible value of $n$?

6 votes
Accepted

If $2^a=3^b$ find $\frac{a}{b}$

1
2 3 4 5
20