Areas

Circle

Círculo A circle is a plane figure, bounded by a single curve line called its circumference, every part of which is equally distant from a point within it, called the center.

A circle sector is any piece of the circle between two radial lines (shaded in both dark and clear grey).

A segment of a circle is the region between a chord of a circle and its associated arc (shaded in dark grey).

An annulus is the region lying between two concentric circles

Areas

$\fs2Circle\;\;\;\;Area=\pi\;\cdot\;r^2$

$\fs2Circle\;sector\;\;\;Area=\frac{\pi\;\cdot\;r^2\;\cdot\;\alpha}{360}$

$\fs2Segment\;of\;a\;circle\;\;\;Area=A_1\;-\;A_2$
$\fs1where\;A_1\;is\;the\;area\;of\;the\;circle\;sector\;OAB\;and\;A_2\;is\;the\;area\;of\;the\;triangle\;OAB$

$\fs2Annulus\;\;\;Area=\pi\;(\;r^2\;-\;r'^2)$

Find the area of the crown which radius are 3 and 9

$\fs2\;(Take\;\pi=3.14)$

Area=