I have a question regarding finding the range of the projectile given the projectile crosses points P1(a,b) and P2(b,a).

I know any point on the projectile curve satisfies following equation:

y = x.tan \{theta} (1- (range/x))

therefore, the only thing remains to be found out is tan \{theta}.

Can anyone please direct me in finding \theta given these two point- P1(a,b) and P2(b,a).

Thanks,

Abhi