1. The problem statement, all variables and given/known data http://imgur.com/BPPbwpu 2. Relevant equations s = ((v + u)*t)/2 - an equation of motion for constant acceleration, which is applicable in this situation. 3. The attempt at a solution Let u be the velocity at which the projectile was launched. It is given that sx = symax. So: sx = symax = u*cos(θ)*t Thus: symax/t = u*cos(θ) Now, in the y-direction, the projectile was given initial velocity u*sin(θ), and at the top of its trajectory (where it has maximum height symax), it has final velocity 0 m/s. Thus: symax = ((0 + u*sin(θ))*t)/2 , which means: symax/t = u*sin(θ)/2 However, since symax/t = u*cos(θ) : u*cos(θ) = u*sin(θ)/2 Thus: cos(θ) = sin(θ)/2 2*cos(θ) = sin(θ) 2 = sin(θ)/cos(θ) 2 = tan(θ) θ = tan-1(2) = 63.4349° However, this was marked wrong. Can somebody see what could have gone wrong? Thank you.