Question

Let Ф1 and Ф2 be the  values of angles of projection such that the horizontal range of the projectile in both cases is equal. Then
A) Ф1 = Ф2  
B) Ф1 + Ф2 = π/2      
C) Ф1 + Ф2 = π/4
D) Ф1 - Ф2 = π/4
answer should come A) AND B)

Answer 1

R = u² Sin 2 Ф / g

So Sin 2Ф1 = Sin 2Ф2

2Ф1 = 2Ф2  or  2Ф1 = 180 - 2Ф2 

Ф1 = Ф2  or  Ф1 = 90 - Ф2