Question

cos (-9π/4)=
ctg (-π/3)=
дам все 50 баллов, срочно, в течении часа плииз​

Answer 1

$Cos(-\frac{9\pi }{4})=Cos(2\pi+\frac{\pi }{4})=Cos\frac{\pi }{4} =\frac{\sqrt{2}}{2}\\\\2)Ctg(-\frac{\pi }{3})=-Ctg \frac{\pi }{3}=-\frac{\sqrt{3}}{3} \\\\3)Ctg\alpha =-2$

$\frac{2Sin\alpha+3Cos\alpha}{5Sin\alpha-Cos\alpha}=\frac{\frac{2Sin\alpha}{Sin\alpha }+\frac{3Cos\alpha}{Sin\alpha}}{\frac{5Sin\alph }{Sin\alpha}-\frac{Cos\alpha}{Sin\alpha}} =\frac{2+3Ctg\alpha}{5-Ctg\alpha}=\frac{2-3*(-2)}{5-(-2)}=\frac{2+6}{5+2}=\frac{8}{7}=1\frac{1}{7}$