Первая скудка D=b^2-4ac=6^2-4×1×8=36-32=4
D=4
X1=6+корен4/2×1=6+2/2=8/2=4
X2=6-корен4/2×1=6-2/2=4/2=2
X1=4
X2=2
А дальше ?
Tg(2x+π/3)=-√3/3;
2x+π/3=arctg(-√3/3)+πk, k∈Z;
2x+π/3=-arctg(√3/3)+πk, k∈Z;
2x+π/3=-π/6+πk, k∈Z;
2x=-π/3-π/6+πk, k∈Z;
2x=-π/2+πk, k∈Z;
x=-π/4+πk/2, k∈Z.
Ответ: -π/4+πk/2, k∈Z.
6+7х=3х^3
-3х^2+7х+6=0
3х^2-7х-6=0
Д = 49+4÷3×6=121
Х1= (7+11)/2= 9
Х2=(7-11)/2=-2