Hi, I wrote the following code 

p := 4*N/(Pi*d^2)
y := (1/2)*b

x := (1/2)*B

And I am trying to expand the following double integral 

M := 4*u*p*(int(sqrt(x^2+y^2), [y, x]))

But I keep getting the error:

Error, (in int) integration range or variable must be specified in the second argument .

When I define B and b just as B and b, the error is gone and it works, but as soon as I add 1/2 to the values, the error occurs. Please help me out here :(