Question 786384
{{{20 sin^2 (x) + 21 sin (x) + 4 = 0}}}

{{{20 sin^2 (x) + 16sin(x)+5 sin (x) + 4 = 0}}}


{{{4sin(x)(5sin(x)+4)+1(5sin(x)+4)=0}}}


(5sin(x)+4)((4sin(x)+1)=0

sin(x)=-4/5 OR sinx=-1/4


Now apply (0,2pi)