As given the formula of range is
[tex]R = \frac{v^2sin2\theta}{g}[/tex]
now for the maximum range
[tex]\theta = 45[/tex]
[tex]R_{max} = \frac{v^2}{g}[/tex]
now for half of this maximum range we will have
[tex]\frac{R_{max}}{2} = \frac{v^2sin2\theta}{g}[/tex]
[tex]\frac{v^2}{2g} = \frac{v^2sin2\theta}{g}[/tex]
now from above we have
[tex]sin2\theta = \frac{1}{2}[/tex]
so two possible values for above is given as
[tex]\theta = 15 degree, 75 degree[/tex]
so above two angle we will have half of maximum range