Area of a Unit Disk

Question

True or false? A unit disk’s area can be evaluated using the Cartesian coordinate system area formula.

I was given this question to answer, and I have no idea what it is asking. What is a unit disk? Assuming it is like the unit circle, can't if find the area with $\pi r^2$? Is this the cartesian system or is it polar?

EDIT

I've now seen the correct answer with the explanation. The answer is True, and this is the reason provided.

Any enlightenment?

Answer 1

The question intends the Cartesian coordinate system area formula to be $$Area=\int y\; \text{d}x$$ where the limits are chosen according to the region you want to find the area of. I guess the point is that you can find a function to describe the (upper half of the) disk using Cartesian coordinates in $y=\sqrt{1-x^2}$ and can integrate that from $-1$ to $1$.