6sin^2x - 5sinx-4=0 [-7 пи /2 ; -3 пи/2]
sinx=a
6a²-5a-4=0
D=25+96=121
a1=(5+11)/12=4/3⇒sinx=4/3>1 нет решения
a2=(5-11)/12=-1/2⇒sinx=-1/2⇒x=-π/6+2πk U sinx=-5π/6+2πk,k∈z
-7π/2≤-π/6+2πk≤-3π/2
-21≤-1+12k≤-9
-20/12≤k≤-8/12
k=-1 x=-π/6-2π=-13π/6
-7π/2≤-5π/6+2πk≤-3π/2
-21≤-5+12k≤-9
-16/12≤k≤-4/12
k=-1 x=-5π/6-2π=-17π/6