<span> 3х^3+2х^2-21х-14=0;</span>
х^2(3х+2)-2(х+7)=0
(х^2-2)(3х+2)(х+7)=0
х^2-2=0 3х+2=0 х+7=0
х^2=2 3х=-2 х=-7
х=+корень из 2 х=-2/3
х=-корень из 2
1)Пропорцией:
70% воды - 100 %
x - 40%
x= (70*40)/100= 28 процентов
![\frac{3x-1}{6} - \frac{x}{3} = \frac{5-x}{9}](https://tex.z-dn.net/?f=+%5Cfrac%7B3x-1%7D%7B6%7D+-+%5Cfrac%7Bx%7D%7B3%7D+%3D+%5Cfrac%7B5-x%7D%7B9%7D+)
Приведем к общему знаменателю:
![\frac{3*(3x-1)}{3*6} - \frac{6*x}{6*3} = \frac{2*(5-x)}{2*9}](https://tex.z-dn.net/?f=%5Cfrac%7B3%2A%283x-1%29%7D%7B3%2A6%7D+-+%5Cfrac%7B6%2Ax%7D%7B6%2A3%7D+%3D+%5Cfrac%7B2%2A%285-x%29%7D%7B2%2A9%7D)
Избавимся от знаменателя ( умножим на 18):
3(3х-1) - 6х = 2 *(5-х)
9х-3-6х=10-2х
3х-3=10-2х
3х+2х=10+3
х=13/5 =2,6
Проверим:
![\frac{3*2,6-1}{6} - \frac{2,6}{3} = \frac{5-2,6}{9} \\ \\ \frac{6,8}{6} - \frac{2,6}{3} = \frac{2,4}{9} \\ \\ ](https://tex.z-dn.net/?f=%5Cfrac%7B3%2A2%2C6-1%7D%7B6%7D+-+%5Cfrac%7B2%2C6%7D%7B3%7D+%3D+%5Cfrac%7B5-2%2C6%7D%7B9%7D+%5C%5C++%5C%5C++%5Cfrac%7B6%2C8%7D%7B6%7D+-+%5Cfrac%7B2%2C6%7D%7B3%7D+%3D+%5Cfrac%7B2%2C4%7D%7B9%7D++%5C%5C++%5C%5C++%0A)
![\frac{20,4 -15,6}{18} = \frac{4,8}{18} \\ \\ \frac{4,8}{18} = \frac{4,8}{18} ](https://tex.z-dn.net/?f=%5Cfrac%7B20%2C4+-15%2C6%7D%7B18%7D+%3D+%5Cfrac%7B4%2C8%7D%7B18%7D++%5C%5C++%5C%5C++%5Cfrac%7B4%2C8%7D%7B18%7D+%3D+%5Cfrac%7B4%2C8%7D%7B18%7D+%0A)
Y=y(x0)+y"(x0)(x-x0)- ф-ла касательной, где y"-производная функции
y(2)= -4+2*2=0
y"(x)= -2x+2
y"(x0)= -2*2+2= -2
y=0+(-2)(x-2)= -2x+4