8. x²-7x-18=0
D=121
![x_{1}= \frac{7-11}{2}=-2](https://tex.z-dn.net/?f=+x_%7B1%7D%3D+%5Cfrac%7B7-11%7D%7B2%7D%3D-2)
![x_{2}= \frac{7+11}{2}=9](https://tex.z-dn.net/?f=+x_%7B2%7D%3D+%5Cfrac%7B7%2B11%7D%7B2%7D%3D9)
Ответ: -2; 9
9.y=2x+8 и
![y= \frac{6-x}{2}](https://tex.z-dn.net/?f=y%3D+%5Cfrac%7B6-x%7D%7B2%7D+)
![2x+8=\frac{6-x}{2}](https://tex.z-dn.net/?f=2x%2B8%3D%5Cfrac%7B6-x%7D%7B2%7D)
⇒ 4x+16=6-x ⇒ 5x=-10 ⇒ x=-2 (абсцисса точки С)
2b(3a+b)-(a-b)b=6ab+2b²-ab+b²=3b²+5ab
0.2(7-2у)=2.3-0.3(у-6)
1.4-0.4у=2.3-0.3у+1.8
1.4-0.4у-2.3+0.3у-1,8=0
-0.1у-2,7=0|*(-1)
0,1у+2,7=0
у=27
Производная от ctgx=
![- \frac{1}{sin^{2}x}](https://tex.z-dn.net/?f=-+%5Cfrac%7B1%7D%7Bsin%5E%7B2%7Dx%7D+)
производная от tg(x+pi/4)
![\frac{1}{cos^{2}x+ \frac{ \pi }{4}}](https://tex.z-dn.net/?f=+%5Cfrac%7B1%7D%7Bcos%5E%7B2%7Dx%2B+%5Cfrac%7B+%5Cpi+%7D%7B4%7D%7D)
получается
![y'(x)=- \frac{1}{sin^{2}x} + \frac{1}{cos^{2}x+ \frac{ \pi }{4}}](https://tex.z-dn.net/?f=y%27%28x%29%3D-+%5Cfrac%7B1%7D%7Bsin%5E%7B2%7Dx%7D+%2B+%5Cfrac%7B1%7D%7Bcos%5E%7B2%7Dx%2B+%5Cfrac%7B+%5Cpi+%7D%7B4%7D%7D)