Question

Cần gấp 3 bài 12,13,14 nhé 

Answer 1

Câu 13 :

\(S_{quạt}=\dfrac{3,14.4^2.7,55}{360}=1,05\left(dm^2\right)\)

Câu 14 :

\(S_{vành.khuyên}=3,14.\left(4^2-3^2\right)\approx22\left(dm^2\right)\)

\(S_{cân.tính}=\dfrac{22}{4}=5,5\left(dm^2\right)\)

Answer 2

Câu 12 :

\(\Delta OAB\) đều \(\left(OA=OB=AB=R\right)\)

\(\Rightarrow\widehat{AOB}=60^o\)

\(\Rightarrow\stackrel\frown{AmB}=60^o\)