x=rcos(θ), y=rsin(θ) Do these formulas look familiar? They give the relationship between two coordinate systems in the plane. Evaluate: |x'r x'θ| |y'r y'θ| I know that the x primes are cos(θ) and -rsin(θ), and the y primes are sin(θ) and rcos(θ), respectively. I am not sure what to do with the matrix. The original functions do look familiar, but I do not remember what they mean.