Ответы и объяснения

2014-03-04T16:48:48+00:00
28.1.
а) sin40sin16=2sin28cos12
б) sin20-sin40=2sin10cos40
в) sin10sin50=2sin30cos20=cos20
г) sin52-sin36=2sin9cos44
28.2
а)cos15+cos45=2cos30cos15=√3 cos15
б) cos46-cos74=2sin120sin14
в) cos20+cos40=2cos30cos10=√3 cos10
г) cos75-cos15=-2sin45sin30=-√2/2
28.3
a)sin \frac{pi}{5}-sin\frac{pi}{10}=2sin\frac{pi}{20}cos\frac{3pi}{20}\\b)sin\frac{pi}{3}+sin\frac{pi}{4}=2sin\frac{7pi}{24}cos\frac{pi}{24}\\c)sin\frac{pi}{6}+sin\frac{pi}{7}=2sin\frac{13pi}{84}cos\frac{pi}{84}\\d)sin\frac{pi}{3}-sin\frac{pi}{11}=2sin\frac{4pi}{33}cos\frac{7pi}{33}