The angle between the thrust vector and the positive x axis is α:
The drag: D = -|D|i +0j. The angle between the weight vector and the positive x axis is (270 - γ);
The equilibrium conditions are
Substitute and collect like terms:
Solve the equations for the terms in γ.
Part (a): Take the ratio of the two equilibrium equations:
Divide top and bottom on the right by |D|.
Part (b): The flight path angle is a negative angle measured from the horizontal, hence from the equality of opposite interior angles the angle γ is also the positive elevation angle of the airplane measured at the point of landing.