Question

Arccos(sin 0,8пи) = ?

Answer 1

$\star \; \; arccos (cosx)=x\; \; \; pri\; \; x\in [\, 0,\pi \, ]\; \; \star \\\\\star \; \; sinx=cos(\frac{\pi }{2}-x)\; \; \star \\\\\\arccos(sin\, 0,8\pi )=arccos (cos(\frac{\pi }{2}-0,8\pi ))=arccos (cos(-0,3\pi ))=\\\\\star \; \; cos(-x)=cosx\; \star \\\\=arccos(cos\, 0,3\pi )= 0,3\pi \in [\, 0,\pi \, ]$