8. (Tracking) Suppose that it is impractical to use all the assets that are incorporated into a specified portfolio (such as a given efficient portfolio). One alternative is to find the portfolio, made up of a given set of n stocks, that tracks the specified portfolio most closely--in the sense of minimizing the variance of the difference in returns Specifically, suppose that the target portfolio has (random) rate of return 71. Suppose that there are 11 assets with (random) rates of return 7, 12,...) We wish to find the portfolio rate of return r = air, twarz + + Onn (with Lima; = 1) minimizing var() - rm). (a) Find a set of equations for the ai's (b) Although this portfolio tracks the desired portfolio most closely in terms of variance, it may sacrifice the mean Hence a logical approach is to minimize the variance of the tracking error subject to achieving a given mean return. As the mean is varied, this results in a family of portfolios that are efficient in a new sense-say, tracking efficient. Find the equation for the x;'s that are tracking efficient