A projection aimed at a mark which is in the horizontal plane through the point of projection falls 'a' cm short of it when the elevation is `alpha` and goes b cm for far when the elevation is `beta` . Show that if the speed of projection is same in all the cases the proper elevation is .

Explanation

`(1)/(2) sin^(-1)[(a sin 2 alpha a+ b sin 2 beta)/(a+b)]`