Recent content by TheEmptySet

  1. TheEmptySet

    MHB Finding the 3rd Number to Keep Variance Unchanged

    Maybe I am misunderstanding something but the way I read the problem was if we have the data set $\{0,2 \}$ we can calculate the mean and variance directly. Now if a new data set is created by adding one other point $\{0,2,y \}$. We can now calculate the new population mean and the new...
  2. TheEmptySet

    MHB Finding the 3rd Number to Keep Variance Unchanged

    The variance is the square root of the sum of the differences from of the data points from the mean so... $\sigma^2=\frac{1}{2}\left[(0-1)^2+(2-1)^2\right]=1$. If we add the new point $y$, we will need to solve the system of equations. $\mu=\frac{1}{3}\left[ 0+2+y\right]$ and...
  3. TheEmptySet

    MHB What is the minimum value of $n$ for a nonnegative polynomial with degree $d$?

    I thought of this in terms of linear algebra and vector spaces. Consider the set \begin{matrix} g_0(x)=\sqrt{c_0} & g_0^2(x)=c_0 \\ g_1(x)=(1+c_1x) & g_1^2(x)=1+2c_1x+c_1^2x^2\\ g_2(x)=\sqrt{c_2}x & g_2(x)=c_1x^2\\ g_3(x)=(x+\sqrt{c_3}x^2) & g_3(x)=x^2+c_3x^3+c_3^2x^4\\ g_4(x)=\sqrt{c_4}x^2)...
  4. TheEmptySet

    MHB Advanced PDE Books: Expert Level Resources

    I used this book Partial Differential Equations of Mathematical Physics and Integral Equations (Dover Books on Mathematics): Ronald B. Guenther,John W. Lee,Mathematics: 9780486688893: Amazon.com: Books It is in its dover days now, but I quite liked it. It is very inexpensive
  5. TheEmptySet

    MHB Solving First-Order PDE: $u_x+2u_y+2u=0$

    Think about the idea behind the method of characteristics. We start by parameterizing the independant variables x and y. x=x(s,t) \quad y=y(s,t) \implies u(x,y)=u(x(r,s),y(r,s)) Now take the derivative with respect to s to get...
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