Concept
Unit circle
2 essays name this object, across 2 fields. What follows is each of them, and the objects they name alongside it.
A sine wave is a circle seen from the side
Sine is introduced as a ratio in a right triangle, which is true and explains nothing about why its graph is a wave. There is a better picture.
Multiplying is turning
Complex numbers are introduced as an algebraic dodge for square roots of negatives. They are better understood as the arithmetic of rotation, at which point every rule stops needing to be remembered.
Named alongside it
The objects these essays reach for when they reach for this one.
PiArgumentComplex exponentialCosineDerivativeImaginary unitModulusPeriodicityRadianRoots of unitySimple harmonic motionSine