DDesmos SAT Prep
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Circle Equations

Graph center-radius form directly and read off circle features visually.

The Desmos trick

Desmos graphs (x-h)^2 + (y-k)^2 = r^2 exactly as written — no rearranging needed. Plot a point to see visually whether it lands inside, on, or outside the circle.

  • Type the equation exactly as given: (x-4)^2+(y+1)^2=49
  • Plot a point as an ordered pair to check its position relative to the circle, e.g. (9,2)
  • The center is read directly from the signs inside each parenthesis (opposite of what's written)

Practice questions

Q1What is the center and radius of the circle (x - 4)^2 + (y + 1)^2 = 49…
Easy
Q2Does the point (9, 2) lie inside, on, or outside the circle (x - 4)^2 …
Medium
Q3What is the center and radius of the circle (x + 2)^2 + (y - 5)^2 = 16…
Easy
Q4Does the point (2, 5) lie inside, on, or outside the circle (x + 2)^2 …
Medium