Let angle of projection is ∅ for which horizontal range and maximum height of a projectile are equal. and u is the intial velocity .
we know,
Maximum Height H = u²sin²∅/2g
horizontal range R = u²sin2∅/g
A/C to question, H=R
So, u²sin²∅/2g = u²sin2∅/g
[ using, sin2x = 2sinx.cosx ]
sin²∅/2 = 2sin∅.cos∅
tan∅ = 4
∅ = tan-¹( 4) or 75.96 degree
angle of projection = tan-¹(4) Ans.