10х + 7 = 8х - 9
10х - 8х = - 9 - 7
2х = - 16
х = - 16 : 2
х = - 8
----------------------------
Проверка: 10 * (-8) + 7 = 8 * (-8) - 9
- 80 + 7 = - 64 - 9
- 73 = - 73
Решение
у = (3 - 2х)∧2
y(5) = (3 - 2*5)∧2 = (-7)∧2 = 49
y(-1/2) =( 3 - 2*(-1/2))∧2 = (3 + 1)∧2 = 4∧2 = 16
2.)
<em>y = 2 - (x+3)²</em>
<em>y = 2 - (x+3)²y = -(x+3)² + 2</em>
- y = x²
- y = (x+3)²
- y = -(x+3)²
- y = -(x+3)² + 2
Пусть s км - длина всего пути
![v_{cp}=\dfrac{s_1+s_2+s_3}{t_1+t_2+t_3}](https://tex.z-dn.net/?f=v_%7Bcp%7D%3D%5Cdfrac%7Bs_1%2Bs_2%2Bs_3%7D%7Bt_1%2Bt_2%2Bt_3%7D)
(км/ч)
![t_1=\dfrac{ \frac{1}{3}s }{100}=\dfrac{s}{300}](https://tex.z-dn.net/?f=t_1%3D%5Cdfrac%7B+%5Cfrac%7B1%7D%7B3%7Ds+%7D%7B100%7D%3D%5Cdfrac%7Bs%7D%7B300%7D)
(ч)
![t_2=\dfrac{ \frac{1}{3}s }{75}=\dfrac{s}{225}](https://tex.z-dn.net/?f=t_2%3D%5Cdfrac%7B+%5Cfrac%7B1%7D%7B3%7Ds+%7D%7B75%7D%3D%5Cdfrac%7Bs%7D%7B225%7D)
(ч)
![t_3=\dfrac{ \frac{1}{3}s }{60}=\dfrac{s}{180}](https://tex.z-dn.net/?f=t_3%3D%5Cdfrac%7B+%5Cfrac%7B1%7D%7B3%7Ds+%7D%7B60%7D%3D%5Cdfrac%7Bs%7D%7B180%7D)
(ч)
![t_1+t_2+t_3=t_1=\frac{s}{300}+\frac{s}{225}+\frac{s}{180}= \frac{s}{15} ( \frac{1}{20}+ \frac{1}{15}+ \frac{1}{12})= \frac{s}{15} * \frac{12}{60} = \frac{s}{75}](https://tex.z-dn.net/?f=t_1%2Bt_2%2Bt_3%3Dt_1%3D%5Cfrac%7Bs%7D%7B300%7D%2B%5Cfrac%7Bs%7D%7B225%7D%2B%5Cfrac%7Bs%7D%7B180%7D%3D+%5Cfrac%7Bs%7D%7B15%7D+%28+%5Cfrac%7B1%7D%7B20%7D%2B+%5Cfrac%7B1%7D%7B15%7D%2B+%5Cfrac%7B1%7D%7B12%7D%29%3D+%5Cfrac%7Bs%7D%7B15%7D+%2A+%5Cfrac%7B12%7D%7B60%7D+%3D+%5Cfrac%7Bs%7D%7B75%7D+)
(ч)
![v_{cp}=\dfrac{s_1+s_2+s_3}{t_1+t_2+t_3}=\dfrac{ \frac{1}{3} s+\frac{1}{3} s+\frac{1}{3} s}{ \frac{s}{75} }=\dfrac{75*s}{s}=75](https://tex.z-dn.net/?f=v_%7Bcp%7D%3D%5Cdfrac%7Bs_1%2Bs_2%2Bs_3%7D%7Bt_1%2Bt_2%2Bt_3%7D%3D%5Cdfrac%7B+%5Cfrac%7B1%7D%7B3%7D+s%2B%5Cfrac%7B1%7D%7B3%7D+s%2B%5Cfrac%7B1%7D%7B3%7D+s%7D%7B+%5Cfrac%7Bs%7D%7B75%7D+%7D%3D%5Cdfrac%7B75%2As%7D%7Bs%7D%3D75)
(км/ч)
Ответ: 75 км/ч.