展開【てんかい】
development, evolution, progression, unfolding, (plot) twist, expansion, spreading out, extending, deployment, building up, expansion (of an algebraic expression), development (of a three-dimensional shape), extraction (of compressed data), decompression, unpacking
発展【はってん】
development, growth, expansion, extension, flourishing, development (of a situation, story, etc.), advancement, progression, unfolding, playing around (sexually; esp. of a male homosexual), having an active sex life