Question

Sin54градусовsin18градусов

Answer 1

$sin54 \times sin18 = \frac{sin54 \times sin18 \times 2cos18}{2cos18} = \frac{sin54 \times sin36}{2cos18} = \frac{sin(90 - 36) \times sin36}{2cos18} = \\ \\ = \frac{cos36 \times sin36}{2cos18} = \frac{0.5sin72}{2cos18} = \frac{0.5sin(90 - 18)}{2cos18} = \frac{0.5cos18}{2cos18} = \\ \\ = \frac{0.5}{2} = 0.25$
Ответ: 0.25