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<br>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∈( $\frac{3}{4}$ ;+∞)