ACT Preparation / Unit 14 ACT 1315 short lesson, about 20 seconds
The Circle Equation
Captions available
The idea
A circle with center (h, k) and radius r is (x − h)² + (y − k)² = r²: the distance formula for every point on it.
In practice
(x − 2)² + (y + 1)² = 16 has center (2, −1) and radius 4.
Where people slip
The right side is r², so 16 means radius 4.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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