1. ## Double integration

Hello, do you mind helping me with this please?

let for some a>0

f(x,y) = a2(cos (x - y) + sin ( x + y)) 0 ≤ x π/2 and 0 ≤ y π/2

Assume without computing a that f(x,y) is the p.d.f of a bivariate random variable ( X,Y) and compute the marginal p.d.f f1(x) and f2(y). Either from f1(x) or f,(y) find the value a > 0 such that f(x,y) is a proper p.d.f
So i need to find a such as the function equals to 1.
i should find 1/2 but i must have forgotten something..

any ideas?

3. ## Re: Double integration

Originally Posted by zeubi94
let for some a>0
f(x,y) = a2(cos (x - y) + sin ( x + y)) 0 ≤ x π/2 and 0 ≤ y [COLOR=#000000][FONT=sans-serif]π/2
$\int_0^{\frac{\pi }{2}} {\int_0^{\frac{\pi }{2}} {\left[ {\cos \left( {x - y} \right) + \sin \left( {x + y} \right)} \right]dydx} } = 4$

4. ## Re: Double integration

Thanks for your answer but do you mind explaining by steps because i am actually stuck somewhere?!

5. ## Re: Double integration

Originally Posted by zeubi94
Thanks for your answer but do you mind explaining by steps because i am actually stuck somewhere?!