0 ≤ Сos²x ≤ 1
0 * (- 3) ≤ - 3Cos²x ≤ 1 * (- 3)
- 3 ≤ - 3Cos²x ≤ 0
- 3 + 1,6 ≤ 1,6 - 3Cos²x ≤ 0 + 1,6
- 1,4 ≤ 1,6 - 3Cos²x ≤ 1,6
Множество значений : y ∈ [- 1,4 ; 1,6]
![a_{9}=1\\ a_{1}+8d=1\\\\ a_{4}a_{7}a_{8}=(a_{1}+3d)(a_{1}+6d)(a_{1}+7d) =\\ (1-8d+3d)(1-8d+6d)(1-8d+7d)=(1-5d)(1-2d)(1-d)\\ f(d)=(1-5d)(1-2d)(1-d)](https://tex.z-dn.net/?f=a_%7B9%7D%3D1%5C%5C%0Aa_%7B1%7D%2B8d%3D1%5C%5C%5C%5C%0Aa_%7B4%7Da_%7B7%7Da_%7B8%7D%3D%28a_%7B1%7D%2B3d%29%28a_%7B1%7D%2B6d%29%28a_%7B1%7D%2B7d%29+%3D%5C%5C%0A%281-8d%2B3d%29%281-8d%2B6d%29%281-8d%2B7d%29%3D%281-5d%29%281-2d%29%281-d%29%5C%5C%0Af%28d%29%3D%281-5d%29%281-2d%29%281-d%29)
Рассмотрим функцию
функция принимает наибольшее значение в точке
Ответ
Скобки раскрой
а^2 *x + 4ax = a + 5x + 5
x( a^2 + 4a - 5) = a + 5
x = (a + 5)/ a(a + 4)