Greetings from Brasil...
According to the properties of the radiation:
X^(a/b) = [tex]\sqrt[b]{X^a}[/tex]
So
X^(2/3) = [tex]\sqrt[3]{X^2}[/tex]
And
Y^(-3/4) = 1/Y^(3/4)
so 1/Y^(-3/4) = Y^(3/4) = [tex]\sqrt[4]{Y^3}[/tex]
Then we get
[tex]\sqrt[2]{X^3} .\sqrt[4]{Y^3}[/tex]
