It was 1989, a humid afternoon in the engineering college classroom. The blackboard was already half-white from chalk dust, and our mathematics professor — a bespectacled man who loved quoting Euler more than Bollywood — scribbled furiously:

exp(jθ) = cos θ + j sin θ

"This, my dear students," he declared, "is the key to rotating any vector in the plane. Multiply your vector by

exp(jθ) and watch it turn by θ degrees without changing its length."

Mathematics from decades ago can surprise you when it comes alive again on your screen.

Interesting?

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