please answer both parts of the question.

1. Explain why any mean-variance optimising investor (i.e., an investor who maximises expected return for a given standard deviation; or who minimises standard deviation for a given expected return) (a) will not hold an inefficient asset or portfolio by itself; (b) but instead will hold a portfolio that lies on the line from the risk-free asset, (E(R), std) = (Rf, 0), tangent to the efficient frontier of risky assets. What is the name of this line? Illustrate your answer using equations and graphs were appropriate