I got 180(60-cos(a)) / root(901-30cos(a)) ... don't know how you got sin(a) on the top, because you differentiate with respect to 'u', not 'a'For the projectile, 66.97 deg <= @ <= 75 deg. For the rates/plane, the first part could be proved using cos rule and Pythagoras, and for the second part I got something that looks like
Though I might have gotten the signs or cos/sins mixed up.