Skip to main content
4 of 15
added 17 characters in body
T. Amdeberhan
  • 43.2k
  • 5
  • 57
  • 217

Let's generalize, and also give explicit solutions.

If $M$ is the $n\times n$ matrix $$M=\left[\frac{1+(-1)^{i+j}}{x_i-y_j}\right]_{i,j=1}^n$$ then the inverse $K:=M^{-1}$ has entries given by \begin{align} K_{a,b}=\begin{cases} 2^n\frac{\prod_{2j-1\neq b}x_{2j-1}-y_a}{\prod_{2j-1\neq a}y_a-y_{2j-1}}\cdot \frac{\prod_{2k-1}x_b-y_{2k-1}}{\prod_{2k-1\neq b}x_{2k-1}-x_b} \qquad \text{$a, b$ are odd} \\ \,\,\,\,\,\,\,\, 2^n\frac{\prod_{2j\neq b}x_{2j}-y_a}{\prod_{2j\neq a}y_a-y_{2j}}\cdot \frac{\prod_{2k}x_b-y_{2k}}{\prod_{2k\neq b}x_{2k}-x_b} \qquad \,\,\,\,\,\,\,\, \text{$a, b$ are even} \\ \qquad \qquad \qquad \,\,\,\,\, 0 \qquad \qquad \qquad \qquad \text{otherwise}. \end{cases} \end{align} The solution to your problem is found by replacing $$x_i=i-1 \qquad \text{and} \qquad y_j=-j.$$ Convention. For instance, when $a$ is odd, the product $\prod_{2j-1\neq b}(x_{2j-1}-y_a)$ is understood as running through all odd integers from $1$ to $n$, excluding $a$.

T. Amdeberhan
  • 43.2k
  • 5
  • 57
  • 217