$\begin{aligned}21.\quad&\textrm{Perhatikan gambar berikut}\end{aligned}$.
$\begin{aligned}\quad\qquad&\textrm{Luas daerah yang diarsir adalah}=\: .... \\ &\text{a}.\quad 154\:\:\textrm{cm}^{\displaystyle 2}\\ &\text{b}.\quad 77\:\:\textrm{cm}^{\displaystyle 2}\\ &\text{c}.\quad 44\:\:\textrm{cm}^{\displaystyle 2}\\ &\text{d}.\quad 38,5\:\:\textrm{cm}^{\displaystyle 2}\\\\ &\textrm{Jawab}:\quad \textbf{d}\\ &\begin{aligned}L_{\displaystyle \text{arsiran}}&=\displaystyle \frac{1}{2}\:\textrm{luas lingkaran}_{\text{besar}}-\textrm{lingkaran}_{\text{kecil}}\\ &=\displaystyle \frac{1}{2}(\displaystyle \frac{1}{4}\pi d^{\displaystyle 2}_{\textrm{besar}})-(\displaystyle \frac{1}{4}\pi d^{\displaystyle 2}_{\textrm{kecil}})\\ &=\displaystyle \frac{1}{2}.\displaystyle \frac{22}{4.7}.14^{\displaystyle 2}-\displaystyle \frac{1}{4}.\displaystyle \frac{22}{7}.7^{\displaystyle 2}\\ &=\displaystyle \frac{22}{28}.(7.14-49)\\&=\displaystyle \frac{22}{28}.49\\ &=38,5\:\: \textrm{cm}^{\displaystyle 2}\end{aligned}\end{aligned}$.
$\begin{aligned}22.\quad&\textrm{Perhatikan gambar berikut}\end{aligned}$.
$\begin{aligned}\qquad&\textrm{Luas daerah yang diarsir adalah}=\: .... \\ &\text{a}.\quad 57\:\:\textrm{cm}^{\displaystyle 2}\\ &\text{b}.\quad 62,8\:\:\textrm{cm}^{\displaystyle 2}\\ &\text{c}.\quad 107\:\:\textrm{cm}^{\displaystyle 2}\\ &\text{d}.\quad 114\:\:\textrm{cm}^{\displaystyle 2}\\\\ &\textrm{Jawab}:\quad \textbf{a}\\ &\begin{aligned}L_{\displaystyle \text{arsiran}}&=\textrm{Luas tembereng doubel}\\ &=2(\textrm{luas juring - luas segitiga siku-siku})\\ &=2\left( \displaystyle \frac{90^{\displaystyle 0}}{360^{\displaystyle 0}}\times\pi.r^{2}-\displaystyle \frac{1}{2}.r^{\displaystyle 2} \right)\\ &=2\left( \displaystyle \frac{1}{4}\pi.10^{\displaystyle 2}-\displaystyle \frac{1}{2}.10^{\displaystyle 2} \right)\\ &=2(78,5-50)=57\:\: \textrm{cm}^{\displaystyle 2}\end{aligned}\end{aligned}$.
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