107

a)
\sphericalangle\left(\overline{u}{,}\ \overline{c}\right)=72°
\sphericalangle\left(\overline{u}{,}\ \overline{d}\right)=0°
\sphericalangle\left(\overline{u}{,}\ \overline{a}\right)=180°
b)
\overline{a}\ alkaa\ pisteestä\ \left(0{,}\ 2\right)
\overline{b}\ alkaa\ pisteestä\ \left(2{,}\ 0\right)
c)
\overline{u}\uparrow\uparrow\overline{d}
\overline{u}\uparrow\downarrow\overline{a}\uparrow\downarrow\overline{b}
\overline{u}\not\parallel\overline{c}\not \parallel\overline{e}