Methods from Change of variables and polar coordinates
All methods from Change of variables and polar coordinates.
Choose and apply a coordinate change
To change variables in a double integral:
- choose new coordinates suggested by the boundaries or by a repeated expression in the integrand;
- solve for and in terms of the new coordinates when needed;
- transform every boundary of the region;
- rewrite the integrand;
- calculate the absolute Jacobian factor;
- integrate over the transformed region.
Good coordinates simplify the region, the integrand or both. A substitution that simplifies the formula but complicates the region may not help.