D= -7+2=-5
a3=a1+2d
a3= -2+2(-5)=-2-10= -12
a4=a1+3d
a4= -2+3(-5)= -2-15= -17
a1+a2+a3+a4= -2-7-12-17= -38
или S4=((2a1+(n-1)d)/2)n= ((-4-15)/2)*4= -19*2= -38
45x+615-6x+18-45+10x=0
49x+588=0
49x=-588
x=-12
![(3x+y-4)^2+(x+y-2)^2=0](https://tex.z-dn.net/?f=%283x%2By-4%29%5E2%2B%28x%2By-2%29%5E2%3D0)
Так как
![(3x+y-4)^2 \geq 0](https://tex.z-dn.net/?f=%283x%2By-4%29%5E2+%5Cgeq+0)
и
![(x+y-2)^2 \geq 0](https://tex.z-dn.net/?f=%28x%2By-2%29%5E2+%5Cgeq+0)
то уравнение верно только при
![\left \{\begin{array}{I} 3x+y-4=0 \\ x+y-2=0 \end{array}}](https://tex.z-dn.net/?f=%5Cleft+%5C%7B%5Cbegin%7Barray%7D%7BI%7D+3x%2By-4%3D0+%5C%5C+x%2By-2%3D0+%5Cend%7Barray%7D%7D)
Решаем
![\left \{\begin{array}{I} 3x+y-4=0 \\ - \\ x+y-2=0 \end{array}}](https://tex.z-dn.net/?f=%5Cleft+%5C%7B%5Cbegin%7Barray%7D%7BI%7D+3x%2By-4%3D0+%5C%5C+-+%5C%5C+x%2By-2%3D0+%5Cend%7Barray%7D%7D+)
![2x-2=0 \\ x=1 \\ \\ 3+y-4=0 \\ y=1](https://tex.z-dn.net/?f=2x-2%3D0+%5C%5C+x%3D1+%5C%5C+%5C%5C+3%2By-4%3D0+%5C%5C+y%3D1)
Ответ:
![(1;\ 1)](https://tex.z-dn.net/?f=%281%3B%5C+1%29)
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