2/3 = 6/9 = 0.(3)
В скобках обозначен период.
Cos287=cos(270+17)=sin17
sin557=sin(540+17)=-sin17
(11sin17+25sin17)/sin17=36sin17/sin17=36
X⁴ + x² - 2 = 0
Сделаем замену x² = m ≥ 0
m² + m - 2 = 0
D = 1² - 4 * 1 * (- 2) = 1 + 8 = 9 = 3²
![m _{1} = \frac{-1+3}{2} =1\\\\m _{2}= \frac{-1-3}{2}=-2](https://tex.z-dn.net/?f=m+_%7B1%7D+%3D+%5Cfrac%7B-1%2B3%7D%7B2%7D+%3D1%5C%5C%5C%5Cm+_%7B2%7D%3D+%5Cfrac%7B-1-3%7D%7B2%7D%3D-2++)
- неуд.
x² = 1
x₁ = 1 x₂ = - 1
Ответ: - 1 ; 1
Обозначим члены геометрической прогрессии через : a ; b ; 36 .
Тогда по свойству геометрической прогрессии : b² = 36a .
Члены арифметической прогрессии : a ; b , 27 , значит : b = (a + 27)/2 .
или 2b = a + 27 .
![\left \{ {{b^{2}=36a } \atop {a=2b-27}} \right.\\\\\left \{ {{b^{2}=36*(2b-27) } \atop {a=2b-27}} \right.\\\\\left \{ {{b^{2}-72b+972=0 } \atop {a=2b-27}} \right.\\\\b^{2}-72b+972=0\\\\D=(-72)^{2}-4*972=5184-3888=1296=36^{2}\\\\b_{1}=\frac{72-36}{2} =18\\\\b_{2}=\frac{72+36}{2}=54\\\\a_{1}=2*18-27=9\\\\a_{2} =2*54-27=81](https://tex.z-dn.net/?f=%5Cleft%20%5C%7B%20%7B%7Bb%5E%7B2%7D%3D36a%20%7D%20%5Catop%20%7Ba%3D2b-27%7D%7D%20%5Cright.%5C%5C%5C%5C%5Cleft%20%5C%7B%20%7B%7Bb%5E%7B2%7D%3D36%2A%282b-27%29%20%7D%20%5Catop%20%7Ba%3D2b-27%7D%7D%20%5Cright.%5C%5C%5C%5C%5Cleft%20%5C%7B%20%7B%7Bb%5E%7B2%7D-72b%2B972%3D0%20%7D%20%5Catop%20%7Ba%3D2b-27%7D%7D%20%5Cright.%5C%5C%5C%5Cb%5E%7B2%7D-72b%2B972%3D0%5C%5C%5C%5CD%3D%28-72%29%5E%7B2%7D-4%2A972%3D5184-3888%3D1296%3D36%5E%7B2%7D%5C%5C%5C%5Cb_%7B1%7D%3D%5Cfrac%7B72-36%7D%7B2%7D%20%3D18%5C%5C%5C%5Cb_%7B2%7D%3D%5Cfrac%7B72%2B36%7D%7B2%7D%3D54%5C%5C%5C%5Ca_%7B1%7D%3D2%2A18-27%3D9%5C%5C%5C%5Ca_%7B2%7D%20%3D2%2A54-27%3D81)
Получили две прогрессии :
9 ; 18 ; 36
81 ; 54 ; 36