Frobenius Definition and 102 Threads

I need to solve a linear, second order, homogeneous ODE, and I'm using the Frobenius method. This amounts to setting: y = \sum_{n=0}^{\infty} c_n x^{n+k} then getting y' and y'', plugging in, combining like terms, and setting the coefficient of each term to 0 to solve for the cn's. This...

Hi I'm in the process of proving a matrix norm. The Frobenius norm is defined by an nxn matrix A by ||A||_F=sum[(|aij|^2)^(1/2) i=1..n,j=1..n] I'm having trouble showing ||A+B|| <= ||A|| + ||B|| thanks for the help