Donner la mesure en radians de chacun des angles :
72°
\(360 \mapsto 2\pi\)
\(72 \mapsto \frac{2\pi}{360}\times 72\)
\(\iff 72 \mapsto \frac{2\pi}{10} \times 2\)
\(\iff 72 \mapsto \frac{2\pi}{5}\)
105°
\(105 \mapsto \frac{2\pi}{360}\times 105\)
\(\iff 105 \mapsto \frac{210\pi}{360}\)
\(\iff 105 \mapsto \frac{21\pi}{36}\)
\(\iff 105 \mapsto \frac{7\pi}{12}\)
20°
\(20 \mapsto \frac{2\pi}{360}\times 20\)
\(\iff 20 \mapsto \frac{2\pi}{36} \times 2\)
\(\iff 20 \mapsto \frac{\pi}{18} \times 2\)
\(\iff 20 \mapsto \frac{\pi}{9}\)
9°
\(9 \mapsto \frac{2\pi}{360}\times 9\)
\(\iff 9 \mapsto \frac{2\pi}{40}\)
\(\iff 9 \mapsto \frac{\pi}{20}\)
30°
\(30 \mapsto \frac{2\pi \times 30}{360}=\frac{60\pi}{360}=\frac{\pi}{60}\)
-45°
\(-45 \mapsto \frac{2\pi \times (-45)}{360}=\frac{-90\pi}{360}=\frac{-\pi}{4}\)