2500:100=х:40; х=2500*40/100; х=1000;
Ответ:цена брюк 1000рублей.
2Cos²x + 5Sinx + 1 = 0
2(1 - Sin²x) + 5Sinx + 1 = 0
2 - 2Sin²x + 5Sinx + 1 = 0
- 2Sin²x + 5Sinx + 3 = 0
2Sin²x - 5Sinx - 3 = 0
Сделаем замену : Sinx = m , где - 1 ≤ m ≤ 1
2m² - 5m - 3 = 0
D = (-5)² - 4 * 2 * (- 3) = 25 + 24 = 49 = 7²
![m_{1}=\frac{5-7}{4}=-\frac{1}{2}\\\\m_{2}=\frac{5+7}{4}=3](https://tex.z-dn.net/?f=m_%7B1%7D%3D%5Cfrac%7B5-7%7D%7B4%7D%3D-%5Cfrac%7B1%7D%7B2%7D%5C%5C%5C%5Cm_%7B2%7D%3D%5Cfrac%7B5%2B7%7D%7B4%7D%3D3)
Sinx = 3 - решений нет
![Sinx=-\frac{1}{2}\\\\1)x=arcSin(-\frac{1}{2})+2\pi n,n\in z\\\\x=-\frac{\pi }{6}+2\pi n,n\in z\\\\2)x=-\pi+\frac{\pi }{6}+2\pi n,n\in z\\\\x=-\frac{5\pi }{6}+2\pi n,n\in z](https://tex.z-dn.net/?f=Sinx%3D-%5Cfrac%7B1%7D%7B2%7D%5C%5C%5C%5C1%29x%3DarcSin%28-%5Cfrac%7B1%7D%7B2%7D%29%2B2%5Cpi+n%2Cn%5Cin+z%5C%5C%5C%5Cx%3D-%5Cfrac%7B%5Cpi+%7D%7B6%7D%2B2%5Cpi+n%2Cn%5Cin+z%5C%5C%5C%5C2%29x%3D-%5Cpi%2B%5Cfrac%7B%5Cpi+%7D%7B6%7D%2B2%5Cpi+n%2Cn%5Cin+z%5C%5C%5C%5Cx%3D-%5Cfrac%7B5%5Cpi+%7D%7B6%7D%2B2%5Cpi+n%2Cn%5Cin+z)
Отрезок не записан.
Если отрезок π < x < 2π , то корни :
![\frac{7\pi }{6} ;\frac{11\pi }{6}](https://tex.z-dn.net/?f=%5Cfrac%7B7%5Cpi+%7D%7B6%7D+%3B%5Cfrac%7B11%5Cpi+%7D%7B6%7D)
4√а² = 2
√ а² = 2 : 4
√ а² = 1/2
( √ а² )² = ( 1/2 )²
а² = 1/4
а1 = 1/2
а2 = - 1/2
ОТВЕТ 1/2 ( или 0,5 ) и минус 1/2 ( или - 0,5 )