= Solution
An <active galactic nucleus> is powered by <accretion> onto a central <supermassive black hole>. Binding-energy release gives $L\sim\eta\dot Mc^2$, so a compact source can outshine its host without converting its entire <mass> into radiation. A disc produces a thermal continuum, a hot corona can Comptonize disc <photons> into X-rays, and surrounding gas produces broad and narrow <emission lines>. Dust can obscure and reradiate the central emission. Orientation explains part of the diversity between unobscured and obscured nuclei, but <accretion> state and intrinsic variability also matter.
<relativistic jets> channel <energy> and <momentum> into collimated magnetized outflows. Disc <rotation> and, in some models, black-hole <rotation> supply the <energy>; magnetic stresses accelerate the plasma and connect the engine to the outflow. <synchrotron radiation> <traces> relativistic <electrons> and <magnetic fields>, while <inverse Compton scattering> can produce higher-energy emission. Bright knots, terminal hotspots and large radio lobes show that the deposited <energy> is not confined to the unresolved nucleus.
For bulk speed $\beta c$ at viewing angle $i$, the <Doppler factor> is $\mathcal D=[\Gamma(1-\beta\cos i)]^{-1}$, and an approaching feature has
$$
\boxed{\beta_{\rm app}=\frac{\beta\sin i}{1-\beta\cos i}.}
$$
Light-travel delay can therefore give <apparent superluminal motion> without any material or <signal> travelling locally faster than light. Beaming also makes approaching jets appear brighter and more rapidly variable; a one-sided image is not proof of a physically one-sided outflow. Spectral, <polarization> and resolved-motion measurements constrain the geometry and emission mechanisms. Jets can inflate cavities and heat surrounding gas, linking <black-hole accretion> to galaxy and cluster feedback.
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