Physics
posted by Max .
The range R of a projectile is defined as the magnitude of the horizontal displacement of the projectile when it returns to its original altitude. (In other words, the range is the distance between the launch point and the impact point on flat ground.) A projectile is launched at t = 0 with initial speed vi at an angle θ above the horizontal. The range is
R = vi2sin2θ/g. What's the launch angle θ at which the maximum range occurs?

When is sinZ maximum? Z=90 degrees. So what is theta at max range?