The equation x5y6=(x+y)11 is homogeneous since both sides have degree 11.
Substituting y=vx:
x5(vx)6=(x+vx)11
v6⋅x11=(1+v)11⋅x11
Cancelling x11 (valid since x>0):
v6=(1+v)11
This equation has no x, so v is a constant.
Since y=vx where v is constant:
dxdy=v
dx2d2y=dxd(v)=0