Given:
sin a= -21/29 , with 3pie/2 <a <2pie
and
tan B= -24/7 ,with pie/2 <B< pie
Find cos(a+b)
\(\frac{3\pi}{2}<\alpha<2\pi\) \(4.712..<\alpha<6.2831..\)
\(sin \alpha=-\frac{21}{29}=0.72413..\)
\(\alpha= arc sin(-\frac{21}{29 })=-0.80978..+2\pi =\color{blue}5.47340..\)
\(\frac{3\pi}{2}<5.47340<2\pi\)
\(\frac{3\pi}{2}<\beta<2\pi\)
\(tan\beta=-\frac{24}{7}=-3.42857..\)
\(\beta=arctan(-\frac{24}{7})=-1.287..+2\pi=\color{blue}4.99618..\)
\(\frac{3\pi}{2}<4.99618<2\pi\)
\(\Large cos(\alpha+\beta)=cos(arcsin(-\frac{21}{29})+arctan(-\frac{24}{7}))\)
\(cos(\alpha+\beta)=cos(5.47340173461+4.99618308959)\)
\(\Large cos(\alpha+\beta)=-0.502068965519\)
!