Answer:
15°, 75°
Step-by-step explanation:
The range of a projectile on level ground is:
R = v₀² sin(2θ) / g
For a range of R/2 at the same initial velocity:
R/2 = v₀² sin(2A) / g
Dividing the second equation by the first:
(R/2) / R = sin(2A) / sin(2θ)
1/2 = sin(2A) / sin(2θ)
sin(2A) = 1/2 sin(2θ)
The maximum range is when θ = 45°.
sin(2A) = 1/2 sin(90°)
sin(2A) = 1/2
2A = 30°, 150°
A = 15°, 75°