А) у= 4х-30
у=4*(-25)-30
у=-100-30
у=-130
б) -6=4х-30
4х= -30+6
4х=-24 /:4
х=-6
Наверно:
(x² +2,5x -18)/(1,5x-6) >1;
(x² +2,5x -18)/(1,5x-6) -1>0
((x² +2,5x -18) -(1,5x-6))/ (1,5x-6)>0 ;
(x² -x-12)/ 1,5(x-4))>0
(x - 4)(x+3)/ 1,5(x-4))>0 * * * x-4≠ 0 ⇔x≠4 * * *
(x+3)/1,5)>0 ;
x+3>0 ;
x >- 3 .
ответ : x∈( -3;∞).
![f(x)=\frac{x}{x^2-4x-21},\; \; \; OOF:\; x^2-4x-21\ne 0\\\\x^2-4x-21=0,\\\\x_1=-3,\; x_2=7\; (teor.\; Vieta)\\\\OOF:\; x\ne -3,\; x\ne 7](https://tex.z-dn.net/?f=f%28x%29%3D%5Cfrac%7Bx%7D%7Bx%5E2-4x-21%7D%2C%5C%3B+%5C%3B+%5C%3B+OOF%3A%5C%3B+x%5E2-4x-21%5Cne+0%5C%5C%5C%5Cx%5E2-4x-21%3D0%2C%5C%5C%5C%5Cx_1%3D-3%2C%5C%3B+x_2%3D7%5C%3B+%28teor.%5C%3B+Vieta%29%5C%5C%5C%5COOF%3A%5C%3B+x%5Cne+-3%2C%5C%3B+x%5Cne+7)
Области определения принадлежит бесконечное множество целых чисел из множества
![D(f)=(-\infty,-3)U(-3,7)U(7,+\infty)](https://tex.z-dn.net/?f=D%28f%29%3D%28-%5Cinfty%2C-3%29U%28-3%2C7%29U%287%2C%2B%5Cinfty%29)