[tex]\it L_{\stackrel\frown{AB}}=\dfrac{2\pi R\cdot u}{360^o}=\dfrac{2\pi \cdot6\cdot u}{360^o}=\dfrac{u}{30^o}\pi \\ \\ \\ a)\ \ L_{\stackrel\frown{AB}}=\dfrac{30^o}{30^o}\pi =\pi\\ \\ \\ b)\ \ L_{\stackrel\frown{AB}}=\dfrac{60^o}{30^o}\pi =2\pi\\ \\ \\ c)\ \ L_{\stackrel\frown{AB}}=\dfrac{90^o}{30^o}\pi =3\pi[/tex]
