Question

How do you graph `x^2 + y^2 = 16` and `r = 4`?

Answer 1

They're the same curve. Recall that `r =sqrt(x^2 + y^2)`.

`sqrt(x^2 + y^2) = 4`

`x^2 +y^2 =4`

Which is same as the other equation. This makes a circle with radius `2` and centre `(0, 0)`. Here is its graph:

graph{x^2 + y^2 = 4 [-10, 10, -5, 5]}

Hopefully this helps!