7. The principal value of the argument of the complex number $1-\sin 100^{\circ}+\mathrm{icos} 100^{\circ}$ is


$7.275^{\circ}$
$$
\begin{aligned}
\text { Original expression } & =1+\cos 170^{\circ}-i \sin 170^{\circ}=2 \cos ^{2} 85^{\circ}-2 i \sin 85^{\circ} \cos 85^{\circ} \\
& =2 \cos 85^{\circ}\left(\cos 85^{\circ}-i \sin 85^{\circ}\right) \\
& =2 \cos 85^{\circ}\left(\cos 275^{\circ}+i \sin 275^{\circ}\right) .
\end{aligned}
$$