ACT Preparation / Unit 14 ACT 1307 short lesson, about 20 seconds
Arcs and Sectors
Captions available
The idea
An arc's length and a sector's area are the fraction θ/360 of the circle's circumference and area, where θ is the central angle.
In practice
A 90° central angle in a circle of radius 4 marks an arc of 2π and a sector of area 4π.
Where people slip
Use the same fraction for both: arc = (θ/360) × 2πr; sector = (θ/360) × πr².
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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