1. 2x^2 + 4x =0
2x(x + 2) = 0
x = 0; x = -2;
2. D = 4 - 4*3*(-8) = 100
sqrt(D) = 10
x1 = (-2-10)/6 = -3
x2 = (-2+10)/6 = 4/3
a1=1
a5=81
1) a5=a1+4d
81=1+4d
4d=80
d=20
2) a2=a1+1d=1+20=21
3) a3=a1+2d=1+40=41
4) a4=a1+3d=1+60=61
Ответ:21;41;61.
<span>sin x = -0.5</span>
x = arcsin(-0,5)
х = - 30°
Вот график этого неравенства: