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Jul
20
answered Solving a system of Differential Equations with RREF'ed Matrix
Jul
20
revised Mathematical Induction — $a_n=2a_{n-1}-1$
more informative title
Jul
20
comment Algebra has me hitting a wall
Hint --- what if you had $(C)(73)-C$?
Jul
20
comment Algebra has me hitting a wall
Sorry, I meant $CD-C=-A$; now do something just to the left side.
Jul
20
comment Solving a system of Differential Equations with RREF'ed Matrix
Differentiate the 2nd equation; eliminate $y''$ from the two equations. Can you solve the resulting differential equation, which has only $x$ in it?
Jul
20
comment Algebra has me hitting a wall
So close.... You got to $CD-C=A$; can you do something to the left side?
Jul
20
comment Prove the following properties of matrices
Or you could just let Angela do the whole problem for you --- then you wouldn't have to think at all.
Jul
20
comment Proving $a\mathbb{Z}\cap b\mathbb{Z}=[a,b]\mathbb{Z}$
I don't know --- I'm not sure why you were given that hint. I'd do it instead by showing that if $x$ is a multiple of $a$ and a multiple of $b$ then it's a multiple of the least common multiple of $a$ and $b$.
Jul
20
answered How can I calculate this exponential growth?
Jul
20
comment Finding original amount in half-life problem
What does $k$ stand for? what does $t$ stand for? How would you use that formula? what would you have to know, and what computation would you do? Full sentences, please.
Jul
20
comment Calculating the number of times a digit is written when given two numbers
What are 51, 52, and so on --- chopped liver?
Jul
20
comment Finding original amount in half-life problem
So, how do you calculate half-life?
Jul
20
comment Finding original amount in half-life problem
What do you know about this kind of problem? Have you not been shown some formulas that might be useful?
Jul
20
comment Converting a distance matrix into Euclidean vector
Have a look at the discussion at mathoverflow.net/questions/97611/…
Jul
20
revised Fibonacci Cubes: $F_n^3 + F_{n+1}^3 - F_{n-1}^3 =F_{3n}$
typo in title
Jul
20
comment Fibonacci Cubes: $F_n^3 + F_{n+1}^3 - F_{n-1}^3 =F_{3n}$
What contest, please?
Jul
20
comment Proving $a\mathbb{Z}\cap b\mathbb{Z}=[a,b]\mathbb{Z}$
Have you not seen the theorem that says that $(a,b)$ can be written as $ar+bs$ for some integers $r$, $s$?
Jul
19
comment number of ways of expressing a number as sum of 5 squares modulo 10
For what it's worth, these numbers are tabulated at oeis.org/A038671 (but for positive $a,\dots,e$).
Jul
19
comment Number of solutions of a linear equation $AX=B$
The nicer way is that if $u$ and $v$ are solutions then so is $u+t(u-v)$ for any real $t$.
Jul
19
comment Type of solutions for the linear equation AX=B
The equation $x+y=17$ can be written as $Ax=b$ with $A$ and $b$ real, but it has the nonreal solution $x=3+i$, $y=14-i$, so your logic is faulty.