Метод подстановки :
x-6y= 25
2x-y=6 ⇔
x=25+6y
50+12y-y=6 ⇔
11y=-44
x=25+6y ⇔
y= -4
x= 25-24 ⇔
x=1
y=-4
x+y= 1+ (-4) = -3
Ответ: -3.
17-2х<span>>0
-2x</span><span>>-17
X</span><span><17/2
</span><span>5x+15<0
5x </span><span>< 15
x</span><15/5
х<span><</span> 3
F(x) = sin²x + cos²x
f(x) = 1
f'(x) = 0.
Ответ: f'(x) = 0.
![\frac{x}{x+2} - \frac{(x-2)^{2} }{2} * (\frac{1}{ x^{2} -4} + \frac{1}{ x^{2}-4x+4 } )=](https://tex.z-dn.net/?f=%5Cfrac%7Bx%7D%7Bx%2B2%7D+-+%5Cfrac%7B%28x-2%29%5E%7B2%7D+%7D%7B2%7D+%2A+%28%5Cfrac%7B1%7D%7B+x%5E%7B2%7D+-4%7D+%2B+%5Cfrac%7B1%7D%7B+x%5E%7B2%7D-4x%2B4+%7D+%29%3D)
Сначала вычислим сумму в скобках
![\frac{1}{ x^{2} -4} + \frac{1}{ x^{2}-4x+4 } = \frac{1}{(x-2)(x+2)} + \frac{1}{(x-2)^2} = \frac{x-2+x+2}{(x-2)^2(x+2)} = \frac{2x}{(x-2)^2(x+2)}](https://tex.z-dn.net/?f=%5Cfrac%7B1%7D%7B+x%5E%7B2%7D+-4%7D+%2B+%5Cfrac%7B1%7D%7B+x%5E%7B2%7D-4x%2B4+%7D+%3D+%5Cfrac%7B1%7D%7B%28x-2%29%28x%2B2%29%7D+%2B+%5Cfrac%7B1%7D%7B%28x-2%29%5E2%7D+%3D+%5Cfrac%7Bx-2%2Bx%2B2%7D%7B%28x-2%29%5E2%28x%2B2%29%7D+%3D+%5Cfrac%7B2x%7D%7B%28x-2%29%5E2%28x%2B2%29%7D+)
Далее умножаем на дробь
![\frac{(x-2)^{2} }{2} * \frac{2x}{(x-2)^2(x+2)} = \frac{x}{x+2}](https://tex.z-dn.net/?f=+%5Cfrac%7B%28x-2%29%5E%7B2%7D+%7D%7B2%7D+%2A+%5Cfrac%7B2x%7D%7B%28x-2%29%5E2%28x%2B2%29%7D+%3D+%5Cfrac%7Bx%7D%7Bx%2B2%7D+)
Получившийся результат отнимаем
![\frac{x}{x+2} - \frac{x}{x+2} =0](https://tex.z-dn.net/?f=%5Cfrac%7Bx%7D%7Bx%2B2%7D+-++%5Cfrac%7Bx%7D%7Bx%2B2%7D+%3D0)