Y=x²-4x-7=(x-2)²-11
(2;-11)- точка минимума
y(-1)=1+4-7=-2
y(2)=-11
y(5)=25-20-7=-2
y∈[-11;-2]
Составим уравнение.
2(3t+1)=10t+18
6t+2=10t+18
-4t=16
t=-4
Ответ: -4
Х-у=8
х=у+8=0
у=8+0=0
ху=8+8=16
ответ :16
По рисунку
![a_{1}](https://tex.z-dn.net/?f=+a_%7B1%7D+)
=1, d=2
![a_{20}](https://tex.z-dn.net/?f=+a_%7B20%7D+)
=?
![a_{30}](https://tex.z-dn.net/?f=+a_%7B30%7D+)
=?
![a_{n} = a_{1} +(n-1)*d](https://tex.z-dn.net/?f=a_%7Bn%7D+%3D+a_%7B1%7D+%2B%28n-1%29%2Ad)
подставляем
![a_{20} =1+(20-1)*2=1+19*2=1+38=39](https://tex.z-dn.net/?f=+a_%7B20%7D+%3D1%2B%2820-1%29%2A2%3D1%2B19%2A2%3D1%2B38%3D39)
![a_{30}](https://tex.z-dn.net/?f=+a_%7B30%7D+)
=1+(30-1)*2=1+29*2=1+58=59
-4(2+3x)+11=-15x-3
8-12x+11=-15x-3
-12x+15x=-3+8-11
-3x=-6
x=-6:(-3)
x=2
Ответ: x=2