What Are the Launch Angles for Half the Maximum Range of a Projectile?

[mullets1200]

Homework Statement

A projectile's horizontal range on level ground is R =v0^2 sin2(theta)/g. At what launch angle or angles will the projectile land at half of its maximum possible range.

The Attempt at a Solution

So what i did was:
Half the range occurs when sin(2θ) = 0.5

So 2θ = arcsin(0.5)...so θ = 0.5*arcsin(0.5) = 15 (degrees)

but when i enter that in it says there is more than one answer, how do i get the other answer?

 

[ehild]

If sin (alpha)=0.5, alpha can be 30 or 180-30 degrees.

ehild