Brainlag Plusx² + y² = r² for a circle centred at the origin, points on it, and the tangent at a point.
x² + y² = r²
Every point (x, y) on a circle with centre (0, 0) and radius r is r away from the origin.
By Pythagoras, x² + y² = r². So x² + y² = 49 has radius 7, and a circle of radius 2.5 is x² + y² = 6.25.
To test a point, work out x² + y². Equal to r²: on the circle. Less: inside. More: outside.
The rest of this lesson and its 7 practice questions are in Plus.
Screen 1 of 3, free to read.
- 7 exam-style questions, marked as you go, each with a worked solution
- The Graphing Calculator beside every question
- Anything you get wrong is saved to your flashcards