A projectile is fired up an incline (incline angle φ) with an initial speed vi at an angle θi with respect to the horizontal (θi > φ). (a.) Show that the projectile travels a distance d up the incline, where d = 2*vi^2*cosθi*sin(θi-φ) / g*cos(φ)^2 (b.) For what value of θi is d a maximum, and what is the maximum value? I was given a hint to get d into the projectile equations by expressing x(final) and y(final) in terms of d and φ. So far I haven't been trying to use that hint, but I can't figure out how... Any help would be highly appreciated.