hi

suppose the body is projected at an angle @with speed u..

then

range = (u)sqr sin2@ /g

therefore sin 2@= rg/(u) sqr

ther is another value sin $ for which

sin $=rg/(u) sqr

therefore sin2@ = sin$

 

therfore either 2@=$

or 2@ = 180 - $

i.e @1 = $ / 2

and @2 = 90 - $/2

 

now take  the 2 values of the angle of projection and find the values of time

take the product and use trigo formula to solve. u'll get the answer as a constant into range

 

im very sorry but finding it very difficult to type the angles and solving