Решите системы неравенств:
81(а,б)
82(а,б,в)

$left { {{6x^2-29x+30 leq 0} atop {5x+2 textgreater 3x^2}} right. left { {{6x^2-29x+30 leq 0} atop {5x+2-3x^2 textgreater 0}} right. ; 6x^2-29x+30 leq 0; D=b^2-4ac; 29^2-4*6*30=121; x_1= frac{-b+- sqrt{D} }{2a}; x_1= frac{29-11}{12}=1,5; x_2= frac{29+11}{12}= 3 frac{1}{3}$ )
x∈[1,5, $3 frac{1}{3}$ ]
$5x+2-3x^2 textless 0; 3x^2-5x-2 textgreater 0; x_3+x_4= frac{5}{3}; x_3*x_4= -frac{2}{3}; x_3=- frac{1}{3}; x_4=2$
x∈(-∞, -1/3)⋃(2, +∞)
Ответ: x∈[1,5;2)

$left { {{x textless 0} atop {21x^2+39x-6 textless 0}} right.; 21x^2+39x-6 textless 0 ; 21x^2+39x-6=0; x_1+x_2= -frac{b}{a} =- frac{39}{21}; x_1*x_2= frac{c}{a} =- frac{6}{21} ; x_1=-2; x_2= frac{1}{7};$
x∈(-2;1/7)
x<0
x∈(-∞, 0)
Ответ: x∈(-2;0)

$left { {{x textgreater 0} atop {4x^2+5x-6 textgreater 0}} right. ; 4x^2+5x-6 textgreater 0; 4x^2+5x-6=0; x_1+x_2=- frac{b}{a}= -frac{5}{4}; x_1*x_2= frac{c}{a}=- frac{6}{4}; x_1=-2; x_2= frac{3}{4};$
x∈(-∞, -2)⋃( $frac{3}{4}$ , +∞)
x>0
x∈(0, +∞)
Ответ: x∈( $frac{3}{4}$ ;+∞)