Б)
![7x - 3y = 13 \\ x - 2y = 5](https://tex.z-dn.net/?f=7x+-+3y+%3D+13+%5C%5C+x+-+2y+%3D+5)
Из второго уравнения выразим х и подставим в первое:
![x = 5 + 2y \\ 7(5 + 2y) - 3y = 13 \\ \\ x = 5 + 2y \\ 35 + 14y - 3y = 13 \\ \\ x = 5 + 2y \\ 11y = - 22 \\ \\ x = 5 + 2y \\ y = - 2 \\ \\ y = - 2 \\ x = 5 + 2 \times ( - 2) = 5 - 4 = 1](https://tex.z-dn.net/?f=x+%3D+5+%2B+2y+%5C%5C+7%285+%2B+2y%29+-+3y+%3D+13+%5C%5C++%5C%5C+x+%3D+5+%2B+2y+%5C%5C+35+%2B+14y+-+3y+%3D+13+%5C%5C++%5C%5C+x+%3D+5+%2B+2y+%5C%5C+11y+%3D++-+22+%5C%5C++%5C%5C+x+%3D+5+%2B+2y+%5C%5C+y+%3D++-+2+%5C%5C++%5C%5C+y+%3D++-+2+%5C%5C+x+%3D+5+%2B+2+%5Ctimes+%28+-+2%29+%3D+5+-+4+%3D+1)
Ответ: (1; -2)
г)
![4x - y = 11 \\ 6x - 2y = 13](https://tex.z-dn.net/?f=4x+-+y+%3D+11+%5C%5C+6x+-+2y+%3D+13)
Из первого уравнения выразим у и подставим во второе:
![y = 4x - 11 \\ 6x - 2(4x - 11) = 13 \\ \\ y = 4x - 11 \\ 6x - 8x + 22 = 13 \\ \\ y = 4x - 11 \\ - 2x = - 9 \\ \\ x = 4.5 \\ y = 4 \times 4.5 - 11 = 18 - 11 = 7](https://tex.z-dn.net/?f=y+%3D+4x+-+11+%5C%5C+6x+-+2%284x+-+11%29+%3D+13+%5C%5C++%5C%5C+y+%3D+4x+-+11+%5C%5C+6x+-+8x+%2B+22+%3D+13+%5C%5C++%5C%5C+y+%3D+4x+-+11+%5C%5C++-+2x+%3D++-+9+%5C%5C++%5C%5C+x+%3D+4.5+%5C%5C+y+%3D+4+%5Ctimes+4.5+-+11+%3D+18+-+11+%3D+7)
Ответ: (4,5; 7)
е)
![25 - x = - 4y \\ 3x - 2y = 30](https://tex.z-dn.net/?f=25+-+x+%3D++-+4y+%5C%5C+3x+-+2y+%3D+30)
Из первого уравнения выразим х и подставим во второе:
![x = 25 + 4y \\ 3(25 + 4y) - 2y = 30 \\ \\ x = 25 + 4y \\ 75 + 12y - 2y = 30 \\ \\ x = 25 + 4y \\ 10y = - 45 \\ \\ x = 25 + 4y \\ y = - 4.5 \\ \\ y = -4.5 \\ x = 25 + 4 \times ( - 4.5) = 25 - 18 = 7](https://tex.z-dn.net/?f=x+%3D+25+%2B+4y+%5C%5C+3%2825+%2B+4y%29+-+2y+%3D+30+%5C%5C++%5C%5C+x+%3D+25+%2B+4y+%5C%5C+75+%2B+12y+-+2y+%3D+30+%5C%5C++%5C%5C+x+%3D+25+%2B+4y+%5C%5C+10y+%3D++-+45+%5C%5C++%5C%5C+x+%3D+25+%2B+4y+%5C%5C+y+%3D++-+4.5+%5C%5C++%5C%5C+y+%3D++-4.5+%5C%5C+x+%3D+25+%2B+4+%5Ctimes+%28+-+4.5%29+%3D+25+-+18+%3D+7)
Ответ: (7; -4,5)
ОДЗ
6x-x²-7>0
x²-6x+7<0
D=36-28=8
x1=(6-2√2)/2=3-√2
x2=3+√2
x∈(3-√2;3+√2)
-|x-3|*log(2)(6x-x²-7)≥0
|x-3|*log(2)(6x-x²-7)≤0
|x-3|≥0 при любом х⇒log(2)(6x-x²-7)≤0
6x-x²-7≤1
x²-6x+8≥0
x1+x2=6 U x1*x2=8
x1=2 U x2=4
x≤2 U x≥4
//////////////////////////////////////////
----------(3-√2)-------[2]----[3]------[4]---------(3+√2)---------------
////////////////////////////// //////////////////////////////////////////
x∈(3-√2;2] U [4;3+√2) U {3}
Вот решения 3 и 4)надеюсь поймете)