1. корень(у) = 1.9
у= 1.9^2= 3.61
2. корень (2y) = 3/4
2y = 9/16
y= 9/32
3. корень(0.5y)=0.8
0.5y = 0.8^2
y= 1.28
4. корень(y/7) = 2/7
y/7 = (2/7)^2
y= 4/7
Sin^2x - 4sinxcosx + a cos^2x=0/cos²x
tg²x+4tgx+a=0
tgx=m
m²+4m+a=0
D=16-4a<0
4a>16
a>4
a∈(4;∞)