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a)
\alpha=2\pi-\frac{2\pi}{7}-\frac{\pi}{5}
\alpha=\frac{70\pi}{35}-\frac{10\pi}{35}-\frac{7\pi}{35}=\frac{53\pi}{35}
b)
\alpha=\pi-\frac{3\pi}{10}
\alpha=\frac{10\pi}{10}-\frac{3\pi}{10}=\frac{7\pi}{10}