Change of variables

• How Does Boltzmann’s Transformation Reduce the Heat Equation?
  See how Boltzmann’s similarity variable reduces the heat equation to an ODE, with the chain-rule derivatives and an error-function example.
• How to Change Variables and Bounds in a Double Integral
  Learn how to transform a double integral correctly: map the region, derive new bounds, include the absolute Jacobian, and check the result.