Question

Б) и в)
Б)cos4acosa+sin4asina/sin3a
В)sin80/2cos40-2sin20 cos20

Answer 1

б)

$\frac{cos4 \alpha cos \alpha + sin4 \alpha sin \alpha }{sin3 \alpha } = \\ = \frac{cos(4 \alpha - \alpha )}{sin 3\alpha} = \\ = \frac{cos3\alpha }{sin 3\alpha} = ctg3 \alpha$

в)

$\frac{sin {80}^{0} }{2cos {40}^{0} } - 2sin {20}^{0} cos {20}^{0} = \\ = \frac{sin {80}^{0} }{2cos {40}^{0} } - sin {40}^{0} = \\ =\frac{2sin {40}^{0} cos {40}^{0} - 2sin {40}^{0} cos {40}^{0}}{2cos {40}^{0} } = \\ = \frac{0}{2cos {40}^{0}} = 0$