3
4sin2x+1/2*2cos2x-4=0
4sin2x+cos2x-4=0
8sinxcosx+cos²x-sin²x-4sin²x-4cos²x=0/cos²x
5tg²x-8tgx+3=0
tgx=a
5a²-8a+3=0
D=64-60=4
a1=(8-2)/10=0,6⇒tgx=0,6⇒x=arctg0,6+πn,n∈z
a2=(8+2)/10=1⇒tgx=1⇒x=π/4+πk,k∈z
4
x1+x2=2
x2=2-x1
7(2-x1)-4x1=47
14-7x1-4x1=47
-11x1=33
x1=-3
x2=2-(-3)=5
c=x1*x2=-3*5=-15