When i derivate I get the last line in the picture to be : ...*(2*a*(sigmai)^2+(2-2a)*(sigmam)^2+2*(1-2a)*covariance) instead of *(2*a*(sigmai)^2+(2a-2)*(sigmam)^2+2*(1-2a)*covariance). How do you change the plus/minus sign in (2a-2)*(sigmam)^2 ?

Consider a portfolio p with a% invested in asset I, and (1-a)% in the market portfolio M: E (Rp) = a * E (R) + (1-a) * E (Rm) om=a? o +(1-a)20m+ 2 a (1-a) Ci, m The derivatives of the portfolio with respect to the weight a are then: @ E (Rp) E(R1) - E(Rm) ( o Op - OVO _ 0 (0) 0 . { [ a? 0} + (1-a)?cm+ 2 a (1-a) (im) *[ 2a o +-20m+ 2 aom+ 2 0im - 4 a 6i,m]