# Minimum variance hedge with more than one asset

My portfolio comprises of 3 assets A,B,C that are correlated and the variance-covariance structure is known. At any given point in time, my position in Asset A say is given to me.

I need to construct a variance minimizing hedge using both B and C, given this position in A.

Basically I am approaching the problem by directly constructing the Variance, as a function of say x and y, the positions in B and C, and minimizing the function by setting the partials w.r.t x and y to 0. This gives me 2 equations in x and y and I can solve them for x and y.

My question is that, is this approach sound? What notion of risk is this really minimizing? I did not explicitly construct a risk model here?

If the variances are known to be $\sigma_0$, $\sigma_1$ and $\sigma_2$ and the correlations are $\rho_{01}$, $\rho_{02}$ and $\rho_{12}$ then you can do exactly as you suggest - write down the variance of the total portfolio as a function of your holdings $x_0$, $x_1$ and $x_2$ and set the partial derivatives with respect to $x_1$ and $x_2$ to zero. You end up with the following matrix equation
$$\left[ \begin{matrix} \sigma_1^2 && \rho_{12}\sigma_1\sigma_2 \\ \rho_{12}\sigma_1\sigma_2 && \sigma_2^2 \end{matrix} \right] \left[ \begin{matrix} x_1\\x_2 \end{matrix} \right] = \left[ \begin{matrix} \rho_{01}\sigma_1 \\ \rho_{o2}\sigma_2 \end{matrix} \right] \sigma_0 x_0$$
which you can solve by inverting the matrix, as long as $\rho_{12}\neq \pm 1$ (ie your hedging assets aren't perfectly correlated or anticorrelated).