Answer:
A double integral can be written as:
[tex]\int\limits {f(x, y)} \, dx dy[/tex]
Now, to do this integral, we first can fix one of the variables, like in this case, we can fix x.
Now, with x fixed, this will be a function of only one variable, y, then we can do the integration over y.
Once the function is integrated over y, we can now do the integration over x.
Then the correct option will be:
" Varying the order variable y"
We keep x fixed, and integrate over the other variable.
