假设tant=b/a,1/cost=√(a^2+b^2)/a
y=asinx+bcosx
=a(sinx+tantcosx)
=√(a^2+b^2)sin(x+t),x=π/6
x+t=π/2
t=π/3,arctana/b=π/6
ax+by+c=0的倾斜角
π-arctan(a/b)=5π/6